THE UNIVERSITY
OF ILLINOIS
LIBRARY
.-2.
1
UNIVERSITY OF ILLINOIS
Agricultural Experiment Station
BULLETIN No. 189
PARASITIC RHIZOCTONIAS IN AMERICA
BY GEOEGE L. PELTIER
URBANA, ILLINOIS, JUNE, 1916
CONTENTS OF BULLETIN No. 189
PAGE
Introduction 283
General Historical Account 283
General Characters of Ehizoctonia 286
Distribution of Ehizoctonia in the United States 292
Distribution of Ehizoctonia in Canada 306
Distribution of Ehizoctonia in South America and the West Indies 306
Distribution of Ehizoctonia in Europe 306
Distribution of Ehizoctonia in India and Australia 308
Plan of Procedure ' 308
Symptoms of Ehizoctonia Disease on Various Hosts. . . 308
Inoculation Experiments 337
Discussion of Inoculation Experiments 358
Growth on Media 364
Measurement of Mycelial Cells 370
Soil Survey of Ehizoctonia 372
Parasitism of Rhisoctonia Solani Kiihn 375
Summary 376
Appendix 378
Bibliography 386
FIG. 1. — CARNATION STEM EOT CAUSED BY EMzoctonia Solani
PARASITIC RHIZOCTONIAS IN AMERICA*
BY GEORGE L. PELTIER, ASSOCIATE IN FLORICULTURAL PATHOLOGY
One of the most serious and troublesome diseases which must be
contended with by carnation growers in this country is the so-called
"stem rot" due to the fungus Rhizoctonia. In 1911 a study of this
disease was undertaken at the University of Illinois by Mr. H. W.(
Anderson, at that time Assistant in Floricultural Pathology and now
Professor of Botany in Wabash College. Since July, 1912, when Mr.
Anderson left, a thoro investigation of those diseases of vegetable,
field, and floricultural crops which are caused by Rhizoctonia has
been conducted by the writer, the primary object being to determine
whether infection is brought about by one or by more than one race or
species of this fungus. The results of this phase of the work are pre-
sented in the following pages. Extensive studies have also been made
of stem rot, with a view to publishing at a later date.
GENERAL HISTORICAL ACCOUNT
The first description of Rhizoctonia was given by Duhamel,33 who in
1728 found it causing a disease of saffron (Crocus sativus) in southern
France. The diseased bulbs were thickly covered with a reddish vio-
let network of hyphae which spread out into the surrounding soil, with
knot-like swellings here and there in the mycelial network. Duhamel
conceived these swellings (tubercules) to be the individual plants and
the hyphae to be the roots, and named the fungus Tiiberoides.
Almost sixty years later (1785) another French investigator, Fou-
geroux de Bondaroy,23 mentioned that asparagus that was grown on
land in which diseased saffron bulbs had been previously grown suf-
fered from this same disease. Bulliard11 in 1791 numbered it among
the Truffles and named it Tuber parasiticum. Ten years afterward Per-
soon82 placed the fungus in the genus Sclerotium and called it Sclero-
tium Crocorum.
De Candolle,24 who discovered a similar disease on lucerne, gave to
the fungus the name Rhizoctonia. Later he distinguished three species,
R. Crocorum, R. Medicaginis, and R. Mali. Nees70 in 1817 referred
"The results presented in this bulletin formed part of a thesis submitted by
the author to the Graduate School of the University of Illinois in partial fulfil-
ment of the requirements for the degree of doctor of philosophy in botany, May,
1915. Revised to date of issuance.
283
284 BULLETIN No. 189 [June,
to a fungus attacking crocus as Thanatophytum Crocorum. This ap-
pears, from his description and figures, to have been Rhizoctonia. A
new species of Rhizoctonia was described in France by Duby20 as Rhi-
zoctonia Allii on Allium ascalonicum. In 1843 Leveille65 noted a simi-
lar Rhizoctonia on Rubia tinctorum, Solarium tuberosum, Pliaseolus,
and Tulipa, without attempting to place it under any particular
species. In 1851 the Tulasne brothers134 classified all the forms of
Rhizoctonia as a single species, Rhizoctonia violacea, a classification
which has been adopted by a number of writers. Rhizoctonia on cro-
cus was reported in Germany in 1858 by Kiihn.64 He also found this
same fungus, which he identified as R. Hedicaginis, on sugar beet. At
the same time he described a new species of Rhizoctonia on potato,
which he clearly distinguished from the above species and to which he
gave the name R. Solani.
In the United States, Rhizoctonia was first reported by Webber137
in 1890 on the roots of alfalfa in Nebraska. He listed the fungus as
Rhizoctonia Medicaginis DC. The first extended account of Rhizoc-
tonia in the United States was given by Pammel,76 who found it caus-
ing a serious disease of beets in Iowa. Later, Atkinson3 observed
Rhizoctonia causing damping-off of cotton seedlings, and following
that, of a number of other kinds of seedlings. In 1901 Duggar and
Stewart32 added a large number of hosts subject to Rhizoctonia attack.
Many observations of other hosts and in new localities have since been
made until at the present time Rhizoctonia has been found on one or
more hosts in practically every state in this country. It has also been
reported from Canada, the West Indies, South America, India, and
Australia, so that it may be regarded as a truly cosmopolitan fungus.
Duggar,8 in an article published since this manuscript was com-
pleted, brings out the fact that the violet root felt fungus, commonly
known in Europe and the United States as R. violacea, should be re-
ferred to as R. Crocorum, (Pers.) DC. He states that unfortunately
this name has priority over the more descriptive name R. violacea.
Under R. Crocorum (Pers.) DC., Duggar lists the following pro-
visional synonymy:
Tuber parasiticum Bull. (1791)
Sclerotium Crocorum Pers. (1801)
Ehizoctonia Crocorum DC. (1815)
Rhizoctonia Medicaginis DC. (1815)
Thanatophytum Crocorum Nees (1816)
Tuber Croci Duby (1830)
Ehizoctonia Rubice Dene. (1837)
Ehizoctonia Dauci Eabenh. (1859)
Ehizoctonia violacea Tul. (1862)
Ehizoctonia Asparagi Fckl. [non Fr.] (1869)
Hypochnus violaceus Eriks. (1913)
•Duggar, B. M. : Ehizoctonia Crocorum (Pers.) DC. and E. Solani Kiihn
(Corticium vagum B. & C.) with Notes on Other Species. Ann. Mo. Bot. Gard.,
2, 403-458, 9 figs., Sept., 1915.
1916] PARASITIC RHIZOCTONIAS IN AMERICA 285
Under R. Solani Kiihn (Corticium vagum B. & C.), the form com-
monly found in this country and to a less extent in Europe, and the
name generally used by American authors, Duggar gives the following
synonymy :
Ehizoctonia Betce Eidam [non Kiihn] (1887)
Ehizoctonia Napcece West. (1846)
Ehizoctonia Eapoe West. (1852)
Hypochnus Solani Prill. & Del. (1891)
Duggar states further that with the evidence at hand a number of
species of Rhizoctonia described from Europe may be excluded from
the genus, while several species are doubtful. He adds that in all
probability the six species described from America, listed in Saccardo,
may also be excluded, altho a more critical study of material is needed.
Many attempts have been made to connect the sterile fungus Rhi-
zoctonia with a perfect stage. Fuckel43 in 1869 stated that the ascomy-
cete Byssothesium circinans Fkl. (LeptospJiceria circinans Sacc.) was
the perfect form. However, beyond the association of these two forms
on decaying stems of Medicago sativa, there were no signs of their con-
nection. The same observation was also recorded by Prunet,90 but again
with no more conclusive proof than the presence of the two forms on
the same plant. Massee66 considered Rhizoctonia as representing the
vegetative condition of Rosellinia, because of the fact that the struc-
ture and color of the mycelium and the general habit of Rhizoctonia
resembles that of the Rosellinia quercina Hartig and other destructive
parasites belonging to that genus. He had no further evidence, how-
ever, to support this supposition.
During the summer of 1913, Cook,20 while examining tubers af-
fected with Rhizoctonia, found a sclerotium that contained a mass of
well-developed asci bearing spores. The mycelium .of the sclerotium
was characteristic of Rhizoctonia and the asci appeared to arise di-
rectly from it ; this point, however, could not be determined with any
degree of certainty.
In 1891 Prillieux and Delacroix89 described a basidiomycete, Hy-
pochnus Solani, and altho at the time they did not associate it with
Rhizoctonia, it has been accepted by a number of European writers in
recent years as the perfect stage of R. Solani.
In 1897 Frank41 reported Rhizoctonia violacea as attacking grape-
vines, and since a Thelephora was found associated with it, he pro-
posed the name Thelephora Rhizoctonice.
In 1903 Rolfs,93 working with the Rhizoctonia disease of potatoes
in Colorado, found constantly associated with this fungus a basidiomy-
cete which Dr. E. A. Burt identified as Corticium vagum B. & C., var.
Solani. He was able to trace the connection between the two forms,
and completed his evidence when he obtained cultures of Rhizoctonia
from single spores of the Corticium stage.
286
BULLETIN No. 189
[June,
Eriksson38 has described a new combination, Hypoclinus viola-
ceus (Tul.) Eriks., which he believes is the perfect stage of Rhizoctonia
violacea Tul. However, beyond association on different plants in
the same field, he appears to have no further evidence to show that
the perfect stage which he found on a number of weeds is connected
with R. violacea, found on a number of root crops.
GENERAL CHARACTERS OF RHIZOCTONIA
The morphological characters of Rhizoctonia Solani Kiihn vary
with the age of the mycelium. The young hyphas branch at an acute
angle from the parent hypha, subsequently lying parallel to it. A
constriction is shown at the point of union, and a septum is generally
laid down a short distance from this point. The threads are colorless
and vacuolate. With age the hyphae lie more at a right angle with the
main axis, showing less constriction. They deepen in color into a yel-
lowish and then a rather deep brown, becoming more or less granular
and empty. (Fig. 2.) Fusion of hyphae is very common and can be
observed in any young culture of the fungus. It occurs either between
hyphae of the same parent mycelium or between hyphae from separate
colonies (Fig. 2).
On many hosts a short tufted or bushy growth of the mycelium
may occur with some strains. This tufted growth is likewise present
FiG. 2, — (1) YOUNG HYPH.*: OP Ehisoctonia Solani; (2) OLD, BROWN, AND EMPTY
OF Rhizoctonia Solani
1916] PARASITIC RHIZOCTONIAS IN AMERICA 287
in cultures of the strains that produce such growth on the host plants.
The tufts are composed of brown hyphae, closely septate, constricted
at the septa, and often branching in an irregular manner.
Sclerotia in cultures first appear as small, soft, white masses of
hyphae. Later they become larger and turn dark and hard. Study of
sclerotia at different ages shows that they are of uniform structure com-
posed entirely of masses of irregular and barrel-shaped cells which
break up into sections of one or several cells (Fig. 3). These shortened
hyphal cells function as conidia and germinate readily under suitable
conditions. Germination generally takes place by the protrusion of a
tube thru the septum of a cell where it has broken away from an adja-
cent cell. In some cases the hyphse of the germinating cells pass thru
adjacent cells, which are apparently empty. Occasionally these irreg-
ular and barrel-shaped cells germinate equatorially instead of at the
poles. After the germ tube has grown out some distance, it becomes
narrowed near the germinating cell and a septum is laid down. The
mycelium then develops in the usual manner (Fig. 4).
The formation of sclerotia in nature is rather common on majiy
hosts. The best known examples are those formed on the potato tuber.
The size and shape of the sclerotia vary considerably. On potatoes
they are small, about 1 to 5 millimeters, and are generally flat. On
carnation plants they may reach a diameter of 5 to 8 millimeters.
When the fungus is grown on soil in pure culture, they become 5 to 6
centimeters in diameter (Fig. 5).
The sporiferous stage of Rhizoctonia Solani was first observed in
this country by Rolfs93 in 1903, on potato stems. It was described by
Burt 94 as Corticium vagum B. & C., var. Solani" In Europe this same
fungus is generally known as Hypochnus Solani Prill. & Del."
Altho the writer has observed Rliizoctonla Solani on seventy-five
species of plants, including weeds and field j vegetable, ornamental, and
floricultural crops, growing under diverse conditions and at different
times of the year, for the past three seasons, it was not until the spring
of 1915 that he found the Corticium stage. It was then observed in
his home garden on bean, beet, radish, potato, parsnip, carrot, chard,
spinach, pea, plantain, and pigweed. This stage was also found on
winter vetch growing on newly plowed land, on carnation plants, and
on a number of annual and perennial plants. In some cases patches of
soil well protected from desiccation were covered with the ashy gray
mycelium of the perfect stage.
•In a recent letter from Dr. Burt, he states : " I do not now believe that there
is even a varietal difference between Corticium vagum B. & C. and that on the
potatoes ; hence I shall drop var. Solani. ' '
bln his monograph on the Thelephoracece, Burt12 limits Hypochnus to resupi-
nate species with colored, echinulate spores, while under Corticium he includes
species always resupinate, which have colorless spores and lack cystidia. Accord-
ing to Burt 's classification, Hypochnus Solani Prill. & Del. becomes a synonym
under Corticium vagum B. & C.
288
BULLETIN No. 189
[June,
FIG. 3. — (1) YOUNG, BARREL-SHAPED CELLS WHICH COMPOSE THE SCLEROTIA OF
Ehizoctonia Solani; (2) OLDER, EMPTY CELLS FROM THE SCLEROTIA
FIG. 4. — GERMINATING SCLEROTIAL CELLS OF Shizoctonin Sohmi
1916]
PARASITIC EHIZOCTONIAS IN AMERICA
289
290 BULLETIN No. 189 [June,
The presence of the Corticium stage seems to depend on climatic
conditions. A cool season with an abundance of moisture is appar-
ently essential for its development in the field. This stage is gener-
ally found on plant .tissues that are perfectly healthy ; it is in no way
injurious to them. Some cases have been found where it had devel-
oped on stems almost cut off by Rhizoctonia, but in no instance has
the writer seen it form directly on a lesion or on injured tissue. (See
Figs. 6 and 7.)
The development of the Corticium stage may be described as fol-
lows : The dark brown hyphae of the sterile stage gather, usually at the
base of the plant, and from them arises an ashy gray mycelium, which
forms a fine network around the stem. The development is usually
faster where a little soil, thrown up by the rains, has formed a film
around the stem. The extent of this fruiting layer varies, but it may
proceed several centimeters up the stem. It is so lightly attached to
the plant that it may easily be rubbed off. As it becomes old, it cracks
and falls off.
The outer hyphae of the fruiting layer bear club-shaped basidia
with four sterigmata and spores. Cystidia are lacking. The spores
are colorless, oval to ovate, and have pointed bases. The usual spore
measurement varies from 9 to 14 /* by 6 to 8 /*.
Cultures of Rhizoctonia from single spores of the Corticium stage
have been obtained both by dilution methods and by the method used
by Rolfs,94 which consists in placing a stem covered with the fruiting
stage over an open petri dish containing a nutrient agar, and allowing
the spores to drop on the agar.
Another fungus belonging to the genus Corticium, C. ochra-
leucum (Noack) Burt (see footnote b, page 287), found in the United
States by Stevens and Hall117'119 on pomaceous fruits, has been care-
fully examined by the writer. The mycelium of this species corre-
sponds in many respects to that of R. Solani and the development of
the perfect stage is similar to the development of the Corticium stage
of that species. It appears that these two species are very closely re-
lated, but are entirely distinct forms.
Duggar," who has had an opportunity to study R. Crocorum
(Pers.) DC. more at length, gives the following description of this
species in his recent work :
"The external, general hyphae are more or less different in form and appear-
ance with age. The younger hyphae are usually dilutely violaceous with a pigment
which may be decolorized by the application of acidulated water. The protoplasm
is dense towards the tips of branches and vacuolated farther away. The hyphae
are somewhat flexuous, branched (sometimes closely), with the branches arising
at right angles to the main hypha, and with a partition wall laid down at not
over 10 fj. distant. With age the hyphae become rigid, somewhat less in diameter,
4—8 ft, the branching is distant, and these branches readily break off at the first
partition wall. At the point of union the diameter is uniform with the main
*See footnote, page 284.
ID 16]
PARASITIC HHIZOCTONIAS IN AMERICA
291
FIG. 6. — GREEN TOMATO SHOWING THE SUPERFICIAL ASHY GRAY MYCELIUM OF Cor-
ticium vagum B. & C. PRESENT AT THE POINT WHERE THE TOMATO TOUCHED
THE SOIL
FIG. 7. — ENLARGED VIEW OF A SECTION OF FIG. 6, SHOWING THE DARK STRANDS OF
HYPH^E AND SMALL, SPHERICAL, BROWNISH SCLEROTIA OF Ehizoctonia Solani
KUHN WITH THE ASHY GRAY NETWORK OF MYCELIUM OF Corticium vagum
B. & C. (5x)
292 BULLETIN No. 189 [June.
hypha. The partition walls are distant, often 120-200 /j. apart. The walls now
possess the violet-brown pigment and in the lumen little or no protoplasm is ob-
servable.
"The internal mycelium is likewise branched, septate, often associated into
loose strands, passing between the cells or traversing them. In the early stages
of the disease, so far as reported, these internal hypha3 are nearly colorless
and are generally of less diameter than those constituting the external mat.
" the hyphae constituting the external mantle may be uniformly dis-
tributed, as is the case usually when the fungus attacks fleshy roots or tubers, or
they may also form a number of aggregates having the appearance of loose or root-
like strands."
The infection cushions are distributed over infected roots. ' ' The external
hyphae are for the most part similar to those of the general mycelium, but there
occur also branches in which the cells are short and swollen, sometimes resembling
a short chain of spores The medullary portion of younger cushions is
made up of finer, almost colorless hyphae, and it is this type which enters — strand-
like — the cortical tissues of the root, destroying particularly the cambium and
younger phloem regions. In the later stages of development it will be found that
the cushions seem to extend considerably into the cortex, and more of the hyphae
are colored."
' ' The true sclerotia are flattened or rounded bodies varying in diameter from
a few millimeters to several centimeters. When mature they are of a deep violet-
brown and are thickly clothed with a persistent velvety felt, externally of the same
color as the root-investing hyphae, but ^darkening further in. Among the surface
hyphae of the sclerotia as well as of the 'infection cushions' are found chains
of enlarged cells quite distinct from the enlarged cells of E. Solani. The sclerotia,
as noted previously, are always connected with the root felt by large hyphal
strands.
" a sclerotium consists of fairly compact tissue made up of cells
often considerably branched and sometimes curiously lobed."
DISTRIBUTION OF RHIZOCTONIA IN THE UNITED STATES
In Table 1 is presented a list of those species and sub-species
which have been reported as being susceptible to R. Solani in the
United States. It is obvious that as long as investigations on this dis-
ease are continued, such a list cannot be regarded as complete or final.
It may be noted that plants belonging to the families AmarantTiacece,
Caryophyllacece, Cruciferce, Leguminosce, Solanaceoe, and Composites
are especially susceptible to this fungus. Under favorable conditions
it can attack plants in these families at any stage, from seedlings or
cuttings to older plants, when grown either in the field or in the green-
house. About fifty important families of flowering plants are repre-
sented, several gymnosperms, and Equisetum, one of the Pterido-
phytes. The list includes a number of monocotyledons, which for-
merly were reported as being not susceptible to Rhizoctonia. Among
the dicotyledons are many annuals and perennials, including herbs
and woody plants, as well as most of the greenhouse and garden
plants, field crops, and weeds.
R. Crocorum, as will be seen in Table la, has been reported so far
in this country from only a few scattered states. It is probable that
as investigations continue this fungus will be found in many other
localities.
1916]
PARASITIC RHIZOCTONIAS IN AMERICA
293
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PARASITIC EHIZOCTONIAS IN AMERICA
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306 BULLETIN No. 189 [June,
DISTRIBUTION OF RHIZOCTONIA IN CANADA
In a letter to the writer, Dr. H. T. Giissow of the Central Experi-
mental Farm, Ottawa, Canada, stated that he had observed Rhi-
zoctonia Solani on potato, pea, sweet pea, and aster. That the stem
rot of carnation also occurs in Canada is shown in a paper read by
John Morgan of Hamilton, Ontario, before the Canadian Horticul-
tural Association at Guelph, in August, 1906.
DISTRIBUTION OF RHIZOCTONIA IN SOUTH AMERICA AND
THE WEST INDIES
The following list of plants reported as susceptible to 'R. Solani
in South America and the West Indies, with character of injury, has
been compiled from Cook's19 Diseases of Tropical Plants:
Bean Damping-off, dry rot of stem, and pod rot
Beet Root disease
Cotton Damping-off and sore shin
Cucumber Damping-off
Lettuce Damping-off
Melon Damping-off
Nursery stock Damping-off
Pea Root and stem rot
Potato On stem and tubers
Seedlings Damping-off
Sweet potato Root rot
Tobacco Seed-bed rot
Tomato Rosette and fruit rot
DISTRIBUTION OF RHIZOCTONIA IN EUROPE
Despite the wide distribution of Rhizoctonia in Europe, the nomen-
clature of the species is in a very confused state. Some writers under-
stand Rhizoctonia Crocorum (Pers.) DC. to include several species,
while others treat it as a separate species including forms with a rich
violet mycelium. This uncertainty extends to the other common species
of Rhizoctonia, so that the European literature on the subject offers
many difficulties. Another fact which adds to the confusion is that
both Rhizoctonia Solani and Rhizoctonia Crocorum attack potato
stems and tubers, and while the symptoms caused by the two fungi can
be easily distinguished from one another in the field, it is another mat-
ter to differentiate between them in literature.
A partial list of the hosts in Europe which are attacked by Rhizoc-
tonia is given below to show the extent of the distribution of this fun-
gus. Only the more important references are mentioned.
Austria Hungary. — Rhizoctonia was first reported in Austria Hun-
gary in 1875 on potato. Later 7?. Crocorum was found on sugar beet,
potato and lucerne, and R. Solani (Corticium vagum), on potato.
1916] PAKASITIC RHIZOCTONIAS IN AMERICA 307
Belgium. — R. Crocorum has been observed in Belgium on sugar
beet, potato, and asparagus.
Denmark. — E. Rostrup,96'97 during the years 1884-1905, reported
Rhizoctonia in Denmark on a large number of hosts, including many
weeds and the roots of several species of forest trees. Among the
cultivated crops mentioned are carrot, clover, lucerne, kohl-rabi, beet,
turnip, sugar beet, and potato. Both R. Solani and R. Crocorum
were observed on the potato. In 1892 Rostrup described a new species
from turnip, which he called Rhizoctonia fusca and which differed
only in one or two essential characters from R. Crocorum, also found
on turnip.
England. — Rhizoctonia was first reported in England on mangel
in 1901, and on potato in 1904. The next year Gussow,48 in an ex-
tended account of this disease, stated that it was due to R. Solani.
Salmon,101 in working on a disease of seakale due to R. Crocorum,
found that it was also able to attack salsify, parsnip, carrot, parsley,
lettuce, and potato.
Finland. — Reuter91 has studied a Rhizoctonia in Finland which
causes a root rot of rye. R. Crocorum has been found on beet.
France. — Between the discovery of R. Crocorum in France in
1728, on crocus, and 1851, a number of hosts, including asparagus,
bean, clover, Citrus, Coronilla, grape, onion, Rubia, Sambucus, and
tulip, were reported.
Germany. — In 1858 Kiihn04 found R. Crocorum on sugar beet in
Germany and described the species R. Solani on potato and carrot.
Eriksson38 states that in Germany in 1893 R. Crocorum appeared
on sugar beet in several places ; on lucerne, in 55 localities on plants
1 to 5 years old ; on potato, in 11 localities ; on asparagus, in 3 locali-
ties ; on hop, in 1 locality ; and also on a few weeds, such as Taraxacum
officinale, Convolvulus arvensis, etc. ; and that in 1894 it was observed
on lucerne, in 77 localities; on potato, in 11 localities; and on red
clover, in 8 localities. The species R. Solani (Corticium vagum) and
R. Strobi Scholtz on white pine, have been) recorded.
Holland. — Dr. Johanna Westerdijk reports both R. Crocorum and
R. Solani as being very abundant on potato in Holland.
Ireland. — Peihybridge 83'55 has shown that both R. Crocorum and
R. Solani are present on potato in Ireland.
Italy. — R. Crocorum has been reported at various times as present
on alfalfa, sugar beet, clover, asparagus, carrot, parsley, chard, the
roots of grape, and many weeds in Italy. Rhizoctonia destruens Tassi
occurs on the roots of Delphinium.
Portugal. — The Rhizoctonia attacking sugar beet has been reported
from two localities in Portugal.
Russia. — R. Solani was reported on potato in Russia in 1899.
308 BULLETIN No. 189 [June,
Sweden. — Eriksson37'39 observed a disease of carrot and beet in
1898 in Sweden, caused by R. Crocorum. He was able to inoculate
this fungus on garden and sugar beet, alfalfa, potato, and many weeds
— Stellaria media, Myostis arvensis, Galeopsis, Titraliit, Erysimum
clieiranthoides, Urtica dioica, and Sonchus sp. In addition to these
hosts Eriksson has reported R. Solani (Corticium vagum) on potato
and R. Crocorum on turnip and kohl-rabi.
DISTRIBUTION OF RHIZOCTONIA IN INDIA AND
AUSTRALIA
Shaw,109 working on the morphology and parasitism of Rhizoctonia
in India, reported Rhizoctonia Solani on peanut (Arachis hypogoea),
cowpea (Vigna catjang), jute (Corchorus capsularis), Dolichos Lab-
lab, Trichosanthes cucumernia, soybean (Glycine soja), mulberry
(Morus alba], sesame, melon roots, cotton, roots of Agave rigida, and
potato.
In Australia, Me Alpine07 found R. Solani very widely distributed
on potato.
PLAN OF PROCEDURE
The main object of the present research was to determine whether
of the culturable forms of Rhizoctonia one or more than one race or
species is present in this country. The work was taken up from the
following standpoints :
1. Symptoms of Khizoctonia disease on various hosts
2. Inoculation experiments
3. Growth on media
4. Measurement of mycelial cells
5. Soil survey
SYMPTOMS OF RHIZOCTONIA DISEASE ON VARIOUS
HOSTS
Following are presented the observations of the writer concerning
the nature of the diseases caused by Rhizoctonia on the various hosts,
together with the principal facts which appear in literature regarding
Rhizoctonia on the more important crop plants in this country.
ALFALFA, Medicago sativa
On March 17, 1914, the attention of the author was called to the
damping-off of young alfalfa seedlings in the agronomy greenhouse
of the Station. Microscopic examination and pure cultures showed it
to be due to Rhizoctonia. The seeds had been sown in rows in pure
quartz sand and kept well moistened. The young seedlings, on ger-
mination, were somewhat crowded, so that the conditions were very
1916] PARASITIC EHIZOCTONIAS IN AMERICA 309
favorable for damping-off. The fungus could be seen extending in all
directions over the surface of the sand.
The fungus found on the diseased alfalfa seedlings was compared
with a fungus obtained from mature alfalfa plants sent from Iowa.
Altho the mycelium of the two forms was characteristic of Rhizoctonia,
it differed in many respects, particularly in the color of the hyphae.
The form on the mature plants was undoubtedly Rhizoctonia Cro-
corum, while that on the seedlings was the common Rhizoctonia Solani.
Rhizoctonia was first reported on the roots of alfalfa from Nebraska
in 1890, by Webber,137 as Rhizoctonia Medicaginis DC. This fungus
was next mentioned on alfalfa as Rhizoctonia violacea, by Heald,57
who found it causing a root rot in a single locality in Nebraska in
1906. In 1908 it was reported by Freeman,42 under the name Rhizoc-
tonia violacea, as spreading rapidly in the alfalfa fields in Kansas.
Freeman described the disease as beginning in different parts of the
field where at first a single plant dies. From these centers of infec-
tion the fungus grows in all directions thru the soil, killing the plants
as it proceeds. Thus circles of steadily increasing radii are formed, at
the edges of which plants in all stages of the disease are found. The
great majority of the plants within the affected areas die, while those
which survive are not vigorous and always lose their main tap roots.
The first external sign of the disease is a yellowing of the plant,
which soon after wilts and dies. The roots of a dead or dying plant
are found to be covered with a violet or brownish red mat of mycelial
strands, or hyphae. In a few cases the tap root is completely rotted.
In less severely affected plants, the cortex of the roots slips off easily
when the plants are lifted from the soil, leaving only the central woody
cylinder. This condition is due to the fungous threads which grow
thru the cortex as far as the cambium layer, which they kill. The
fungus forms sclerotia, which may live in the soil for several years.
Stewart126 in 1908 mentioned a root rot and damping-off of alfalfa
in the field in New York. His description of the disease agrees in
some respects with the one given by Freeman. Later he also noticed
the damping-off of alfalfa seedlings in the greenhouse. He was not
certain that Rhizoctonia Crocorum was present in New York, and was
of the opinion that the fungus causing the damping-off of seedlings
in the greenhouse was different from the one found in the field.
Heald,58 in a later article (1911), described more fully the disease
occurring in Nebraska. At that time he regarded the fungus as iden-
tical with Rhizoctonia Medicaginis DC. of Europe.
From the above accounts it is certain that there are two species of
Rhizoctonia in this country able to attack alfalfa — R. Solani, widely
distributed, causing only a damping-off of seedlings, and R. Crocorum,
with a limited distribution, attacking as a rule only mature plants
in the field. At present this latter species has been reported on alfalfa
from Nebraska, Kansas, Iowa, and Virginia.
310 BULLETIN No. 189 [June,
ALTERNANTHERA, Telantliera sp.
In the fall of 1912 cuttings from alternanthera, coleus, and salvia
plants which had been placed in the same bench were found to be
damping-off. A microscopic observation and pure cultures from dis-
eased cuttings showed that RMzoctonia Solani was the causal organism.
Later the fungus was found on alternanthera plants in the field, but
apparently it caused no injury there.
Alternanthera plants grow low and bushy, and thruout the sum-
mer, no matter how dry the season, the soil underneath is usually
moist. On close examination of the tangled mass of branches, strands
of a fungus, which were later found to be made up of bundles of
hyphae, could be seen spreading in all directions. At first glance the
masses of mycelium looked very much like old spider webs. A number
of different varieties of alternanthera were examined, and all were
found to have the characteristic brown strands ramifying upon the
surface of the whole under side of the plant. The reddish varieties
seemed to have more of the fungous strands than did the green and
variegated plants. Cultures from the brown strands in every case
yielded pure cultures of Rhizoctonia which corresponded morphologi-
cally and physiologically to the Rhizoctonia obtained from the cut-
tings.
Whether the fungus was at any time parasitic on the plants in the
field was questionable. However, cuttings made from them still con-
tained pieces of mycelium, and when placed in sand in the greenhouse,
the fungus did parasitize not only the alternanthera cuttings but others
as well.
The belief that Rhizoctonia is present on the branches of the alter-
nanthera plant thruout the year was corroborated in 1913 and again
in the fall of 1914, when the cuttings made from plants in the field
began to damp off in the cutting bench. Repeated observations showed
that the fungus was present on the plants in the field, notwithstanding
the fact that they had been planted in new soil. Old plants brought
in from the field were cut close to the roots and planted in flats in the
greenhouse. These sprouted and developed new shoots, from which
cuttings were made. Many weeds came up in the flats during the win-
ter, and in March both the cuttings and the weeds became infected
with Rhizoctonia. It seems, therefore, that the fungus is present on
alternanthera at all times of the year, tho the only injury it causes is
damping-off of cuttings in the greenhouse.
ALYSSUM, SWEET, Alyssum odoratum
During June, 1914, when the bedding and decorative plants were
being set out from the floricultural greenhouses of the Station, about
1916] PARASITIC RHIZOCTONIAS IN AMKRICA 311
twenty-five plants of sweet alyssum growing in two and one-half inch
pots were found to be diseased. The plants were tall and had fallen
over from their own weight, so that they formed a mat over the pots.
On close examination the soil and plants were found to be covered
with the strands of brown mycelium which are characteristic of E.
Solani. A number of these plants died, while on the stems of others
the fungus formed small lesions near the surface of the soil. The fun-
gus continued to grow on diseased plants placed in the field, and
killed a few more of them.
AMARANTHUS
Specimens of Rhizoctonia on AmarantJius retroflexus were received
from Mr. W. H. Burkholder of Cornell University. The mycelium of
the Corticium stage could be easily recognized on the stems, while the
Rhizoctonia stage was plentiful on the lower part of the plant. A cul-
ture was obtained from scrapings made from the mycelium of the Cor-
ticium stage. Several spores were found and one basidium showing
the four sterigmata was observed.
Duggar and Stewart32 reported the occurrence of Rhizoctonia on
Amaranfhus retroflexus (pigweed) and A. albus (tumble-weed) in
New York in 1901. Several years later Rolfs95 found the perfect
stage, Corticium vagum, in Florida on A. retroflexus and A. spinosus.
ASPARAGUS, ORNAMENTAL, Asparagus sprengeri
Duggar and Stewart32 observed the effects of Rhizoctonia on a
number of plants of ornamental asparagus. They found that the
plants were killed and that many of the leaves were bound to each
other by the brown threads of the Rhizoctonia hyphge.
ASTER, CHINA, CallistepTius Jiortensis
Damping-off of aster seedlings was noticed in flats in the floricul-
tural greenhouses in the spring of 1913 and again in 1914. The dis-
ease first appeared as a small, brown spot on one side of the seedling
at the surface of the soil. This lesion increased in size until the seed-
ling fell over. After a number of seedlings were prostrated, the fun-
gus spread over them, and in time a mat of mycelium covered the sur-
face of the soil.
In May, 1914, a number of aster plants, four to five inches high,
were planted in old soil in which several varieties of carnation plants
had been growing during the winter. There had been more or less
stem rot among these plants all the season. After a month, when the
aster plants were about 6 inches high, they began dying off and con-
tinued to die until they were from 9 to 12 inches high and ready to
312
BULLETIN No. 189
| J tine.
bud. Other aster plants set in new soil at the same time that these
were transplanted developed normally with no stem rot whatever.
TABLE 2. — MORTALITY .OF DIFFERENT VARIETIES OF ASTER GROWN IN OLD CARNA-
TION SOIL INFECTED WITH Khizoctonia Solani
Variety
Number of
plants
Total
dead
Total
healthy
Queen of the Market
50
1
49
Lavender
50
1
49
Azure Blue
50
4
46
Purple '
50
7
43
Pure White
100
13
87
Shell Pink
50
2
48
Eose Pink
50
0
50
Deep Eose
50
0
50
Crimson . .
50
1
49
As can be seen from Table 2, plants from all but two of the varie-
ties died in the bench. The varieties Azure Blue, Purple, and Pure
White were planted where most of the stem rot on the carnations oc-
curred ; hence the higher number of diseased plants in those varieties
is due to location rather than to varietal susceptibility to Rhizoctonia.
Obviously the Rhizoctonia causing carnation stem rot was in this
case able to attack healthy aster plants. The stem rot of these plants
was typical and very similar to the rot of carnations. The first sign
of the disease was a yellowing and drooping of the foliage, followed,
sooner or later, depending on weather conditions, by a sudden wilt-
ing of the whole plant. When the plant was pulled, the bark of the
stem near the surface of the soil would slough off, leaving only the dis-
colored woody tissues.
A stem rot of aster due to Rhizoctonia has been reported only once
before in this country. Duggar and Stewart32 in 1901 found the my-
celium in the tissues of aster and later isolated a pure culture from
them. They observed the disease in a number of localities in New
York during that summer.
BEAN, Phaseoliis vulgaris
The damping-off of young bean seedlings by R. Solani, which
has been observed in the greenhouse and in the field, is characterized
by the production of small lesions at the surface of the ground either
on one side of the stem or girdling it, followed by the falling over and
death of the seedling.
When the fungus attacks older bean plants, lesions of various
sizes are produced just below the surface of the ground, at the surface,
or one or two inches above it. In some plants these discolored spots
can be found on the larger roots also. The lesions, as a rule, have a
1916}
PARASITIC EHIZOCTONIAS IN AMERICA
313
FIG. 8. — STEMS OP MATURE BEAN PLANTS WHICH HAD BEEN PLACED IN A BENCH
IXFECTED WITH Ehizoctonia Solani ORIGINALLY OBTAINED FROM
CARNATION PLANTS
reddish brown band with a lighter colored, sunken area, and extend
thru the cortical layer into the woody tissues. As on the young seed-
lings, the spots are usually localized on one side of the stem, but in
some cases one lesion may girdle the plant. These lesions weaken the
stem and cause it to break off easily.
The first account of Ehizoctonia causing a disease of bean was given
by Atkinson.4 He reported that during the winter of 1894-95 it
caused damping-off of bean seedlings and attacked plants that were
from 6 to 10 inches high. He referred to this form as "the sterile
fungus," and stated that its most characteristic peculiarity was the
mode of branching.
In 1901 Duggar and Stewart32 reported this fungus, from New
York, as the cause of a stem-rot disease of red kidney beans in the field
and of a damping-off among seedling beans in the greenhouse.
314 BULLETIN No. 189 [June,
In 190-1: Hedgcock60 reported as follows:
"The bean crop in the vicinity of St. Louis was severely injured by a Khi-
zoctonia which attacked the stems and large roots of the plant and also produced
brown sunken areas on the surface of the pods, penetrating the latter and discolor-
ing the seeds. An examination of a number of seeds whose surface was discolored,
disclosed the fact that the mycelium of the fungus had established itself in the
second coat and in many instances had formed minute sclerotia there without rot-
ting the seed or even penetrating the cotyledons. The presence of the fungus did
not prevent the germination of the seed. ' '
Fulton44 in 1908 showed that Rhizoctonia from infected pods
caused damping-off of seedling beans and of month-old plants.
A serious outbreak of the stem rot of beans was reported from New
York by Barrus9 in 1910. He found that in some fields as many as
30 percent of the plants were infected. In the same fields during the
following season it caused the, death of at least 5 to 6 percent of the
seedlings ; later in the season, after a rainy spell, a large percentage
of the pods in contact with the ground became infected.
BEET, Beta vulgaris
Young seedlings of the garden beet, in flats, were found damping
off in the vegetable-gardening greenhouses of the Station, July 10,
1913. Cultures showed that R. Solani was the sole cause of the dis-
ease. Characteristic lesions were found on the beets at the surface of
the ground, and strands of mycelium could be plainly seen spreading
out on the surface of the soil.
As with root rot of other fleshy crops, the fungus gains its first
held at the crown of the mature plant, which, as a rule, is just below
the surface of the ground. The first evidence of the disease is a
darkening of the leaf bases, followed by the rotting of the crown.
The leaves retain their color for a long time, or until the leaf stalks
rot off almost completely. With the rotting at the crown, the beets
begin to crack from this point. While the tissues around the cracks
remain firm, as a rule, for a long time, the crown is usually soft, a
condition due to the entrance of other organisms. Lesions are some-
times formed on the sides of the beets, often extending deep into_ the
tissues. When weather conditions become unfavorable to the fungus,
the rotting and cracking stops and the plant may recover from the
attack. The disease is generally scattered thru the field, only a few
plants in a given area being affected.
Under the name Rhizoctonia beta? Kiihn, Pammel70 in 1891 de-
scribed a root rot of sugar beets. He was the first investigator to re-
port serious damage caused by Rhizoctonia in this country. Duggar28
in 1899 regarded the root-rot disease of sugar beet due to Rhizoctonia
as one of the important diseases of that plant. At the present time
this disease is very widespread and is the cause of considerable loss,
especially in irrigated regions.
1916]
PARASITIC UHIZOCTONIAS TN AMERICA
315
FIG. 9. — GARDEN BEET INOCULATED WITH ' Bhizoctonia Solani FROM CARNATION,
SHOWING A LATE STAGE OP INFECTION (Experiment 8)
Damping-off of sugar-beet seedlings has been reported by Selby,108
from Ohio, and by Smith,113 from California.
BEGONIA
Mr. H. W. Anderson in 1911 found a number of begonia cuttings in
the floricultural greenhouses that were damping off badly because of
Rhizoctonia infection. The symptoms were similar to those described
for cuttings of alternanthera.
Damping-off of begonia cuttings has also been observed in New
York by Duggar and Stewart,32 and in North Carolina by Stevens and
Wilson.122
BLACKBERRY, Eubus sp.
Root disease of blackberry and raspberry caused by Rhizoctonia
has been reported only once in this country. Paddock 7r> of Colorado,
who studied this disease, described it as follows :
' ' The trouble was first noticed by the foliage becoming light green or yellow-
ish. Later in the season leaves on occasional plants began to curl and shrivel as
parts of the plant below ground were attacked, but the greatest injury occurred on
the canes above the crown. Here the bark was discolored and shrunken from the
crown to the surface of the soil, or a short distance above. The fungus grew out
within the bark, destroying the tissues, and interfering with the movements of
plant food. The injury commonly extended around the cane, and when it became
deep enough to cut off the supply of moisture and food, the plant died. ' '
BUCKWHEAT, Fagopyrum esculentum
In 1911 Stevens and Wilson120'121 mentioned a serious outbreak of
Rhizoctonia on buckwheat in the western part of North Carolina. No
description of the disease was given.
316
BULLETIN No. 189
[June,
CABBAGE, Brassica oleracea
Atkinson,4 in 1895, in his article on damping-off diseases, men-
tioned cabbage seedlings as being susceptible to damping-off by Rhi-
zoctonia.
Duggar and Stewart32 in 1898 received from Illinois specimens
of cabbage seedlings which had been diseased by Rhizoctonia. They
found that the disease sometimes affected very young seedlings, caus-
ing damping-off, but that it was more common after the plants had
developed one or two true leaves. In the latter instances, small lesions
at or below the surface of the soil characterized the disease. Later,
Duggar and Stewart found
Rhizoctonia causing a sim-
ilar disease of cauliflower
seedlings in New York.
The plants showed ulcera-
tion at the bases of the
stems, the entire cortex in
some cases having disap-
peared.
Fawcett40 reported a
stem rot of cabbage seed-
lings due to Corticium va-
gum B. & C., in Florida, in
1909. According to his
description, the disease
was a typical stem rot,
with a softening of the epi-
dermis followed by a shriv-
FIG. 10. — STEMS OF YOUNG
CABBAGE PLANTS INOCU-
LATED WITH Rhizoctonia
Solani FROM CARNATION
FIG. 11. — STEM OF AN OLD CABBAGE
PLANT WHICH HAD BEEN PLACED IN
A BENCH INFECTED WITH Ehizoc-
tonia Solani FROM CARNATION (Ex-
periment 9)
PARASITIC RHIZOCTONJAS IN AMERICA 317
eliiip of the outside tissues and a browning of the leaves. However,
the plants so affected did not wilt down entirely, and many of them
recovered.
CANDYTUFT, Iberis sp.
During June, 1914, a few plants of candytuft that had been grow-
ing in three-inch pots in the floricultural greenhouses, rotted off at the
surface of the ground. The symptoms were similar to those described
for sweet alyssum. Microscopic examination of diseased tissue re-
vealed R. Solani in every case. Dense masses of hyphse covering the
leaves and stems of these plants were plainly visible.
Duggar and Stewart32 in 1901 reported damping-off by Rhizoctonia
of cuttings of candytuft in New York.
CARNATION, Dianihus caryophyllus
Rliizoctonia Solani attacks carnation plants of all ages, both in the
field and in the greenhouse, causing not only stem rot, but damping-
off of cuttings, of which it is one of the principal causes.
The symptoms of stem rot of carnation are very characteristic of
the effects of R. Solani (Fig. 1). The fungus usually attacks the
stem of the plant at the surface of the ground or occasionally just
above or below. As a rule, the first indication of the disease is a pale
green color of an entire plant or of a single branch. This lighter color
can be noticed in most cases for several days before the actual wilting
takes place. During cloudy weather the plant does not wilt for two
weeks and sometimes for even longer, altho the stem may be almost
completely rotted ; in sunny weather wilting occurs much sooner.
If the stem of a plant that shows the first sign of wilting is pressed
just at the surface of the soil, a soft place is felt and a slight twist is
sufficient to slough off the bark. Beneath this is a slimy, wet area,
which gives this rot its characteristic name. Sometimes, however, the
stem is dry at the point of attack, and upon being broken off, the fibers
appear to be separated and stringy.
The fungus enters the cracks in the corky layer of the bark and at-
tacks the cambium layer, causing the sloughing off of the bark. It
then penetrates the woody tissues, and can be found even in the pith.
The plant may remain alive after the cambium layer is destroyed until
the fungus plugs the vessels. If a diseased plant is left in the soil for
some time, the mycelium overruns the stem, and dark, round sclerotia
are formed either directly on the bark or in the crevices, or cracks.
The Rhizoctonia disease of carnation has been known to florists
ever since carnations have been grown as a commercial crop in the
greenhouse. In Volume I of the American Florist, 1886, is found the
following paragraph, \vhich is probably the first published statement
concerning the stem rot of carnation in this country.
" In a few days plants began to show signs of wilting, and upon examination
I found them rotted off just at the top of the ground, tho half an inch under
the ground the stems appeared perfectly healthy. ' '
318
BULLETIN NO. 189
[June,
1916] PARASITIC RHIZOCTOXIAS IN AMERICA 319
While the cause of the disease was not known at that time, from
the description of the symptoms it is not to be doubted that it was due
to Rhizoctonia.
A great loss of plants from stem rot occurred thruout the country
about 1900. Below are given a few excerpts from notes on this dis-
ease which have appeared during the last thirty years, some of which
agree with our present-day ideas:
1886. "Deep planting causes the disease in many houses."
' ' In our opinion high temperature and deep planting have much to do with
the disease. ' '
1898. ' ' The most dangerous disease that attacks the carnation. Some varie-
ties appear more subject to this disease than others, and there is considerable
complaint about Flora Hill and Silver Spray this season. The most common
error that very often leads to this disease is too deep planting. The plants should
never be planted deeper than they stood in the field, preferably not so deep. The
stem of the plant should be out of the ground sufficiently to hold the branches
away from the soil. I believe this disease is not found on carnations alone, but
on other plants too, and the spores of this fungus may have been embedded in the
soiP, carried over or imprisoned, dormant in the plant from the cutting bench.
' ' To check and prevent the spreading of this disease, dust flour of sulfur
over the plants, and shake them so it will lodge on the stem and branches and on
the soil around the stem. ' '
1900. "Climatic conditions rather than anything else are the chief causes of
the trouble. High ranges of temperature whether in the cutting bench, field, or
house, the results are the same, the amount of rot varying with preceding condi-
tions. Thus, after heavy rains inducing soft growth, a rise of temperature into
the 90 's is a capital condition for the development of stem rot. Some varieties
are also more susceptible to attacks than others, the woodier ones being able to
withstand it more than those of soft growth. ' '
1904. ' ' Stem rot is due to allowing plants to become pot-bound.
' ' Rich soil with too much manure causing a rapid growth causes stem rot.
I believe this to be responsible for more stem rot than all other conditions com-
bined. Too deep planting also favorable for stem rot. Water when absolutely
necessary and then water thoroly. ' '
1906. "Presence of wounds on the bark, or punctures made by insects;
faulty planting; sour or too highly enriched soil; lack of drainage; careless cul-
tivation; lack of fresh circulating air; the maintenance of too great heat com-
bined with atmosphere heavily charged with stagnant moisture during the time
when the outdoor stocks are housed, will cause stem rot to become severe in the
benches. ' '
1907. ' ' Stem rot is the most dreaded and only disease of carnations in the
South. ' '
1909. "Stem rot more dreaded in South than in North."
1911. "Fresh air, plenty of circulation, a sweet soil, and proper watering
will avoid to a great extent the appearance of stem rot or stop its spread. Weather
conditions seem to play an important part, and in most cases as soon as cold
nights are the rule, our troubles grow less. The greatest benefit is derived thru
a clear and rather dry atmosphere. Deep planting not so important. Too much
manure not necessarily a cause of stem rot.
"Stem rot is more prevalent in sour soils than others. The surface of the
soil should be kept open by frequent scratching. A dry interior and a wet surface
is very conducive to stem rot. ' '
1913. "Stem rot in the South is more serious than in the North."
The following older carnation varieties have beeen reported as being
especially susceptible to stem rot : La Purite, Crimson King, De Graws,
Sewan. Flora Hill, Silver Spray, McGowan, Portias, Scott, Jubilee,
320 BULLETIN No. 189 [June,
Craig, Boston Market, Crane, Lawson, Lady Bountiful, Winsor. Sev-
eral of these varieties are still propagated by a few growers and with
good success, but the majority of them have been discarded. Of the
newer types no one seems to be more susceptible than the others.
To Duggar and Stewart30 is owed the discovery that Rhizoctonia
is the cause of stem rot of carnation. This they proved conclusively
in 1899 by inoculation experiments with pure cultures, repeated many
times. Duggar and Stewart state that this stem rot is one of the most
troublesome of the carnation diseases and probably occurs thruout the
United States wherever the carnation is grown. Stewart123'124 at the
same time distinguished between two distinct diseases, both called
' ' stem rot. ' ' One is caused by Rhizoctonia, and the other by Fusarium.
Card and Adams13 of Rhode Island studied methods of control of
both Fusarium and Rhizoctonia rots. They came to the conclusion
that the use of clean, fresh sand in the cutting bench helps to control
the fungus. They also found that stable manure does not favor, the
spread of the disease.
In 1902 Stone and Smith129 reported carnation stem rot in Massa-
chusetts. Two years later Clinton14 reported the presence of the
disease in Connecticut. In 1906 Heald57 stated that it was found in
the field and in the greenhouse near Lincoln, Nebraska. Blake and
Farley10 in New Jersey conducted a number of soil experiments for
the control of stem rot.
CARROT,. Daucus carota
Occasionally R. Solani causes damping-off of carrot seedlings,
but the plants seem to be more susceptible later, when the fleshy root
is formed. Here the rot starts at the crown and works up into the leaf
bases. It also progresses into the interior of the fleshy root, as a rule
showing no signs on the exterior for some time. In some cases lesions
are found on the exterior of the carrot and on the larger secondary
roots where they branch from the fleshy part.
Duggar and Stewart32 were the first to find a disease of carrot due
to Rhizoctonia. In 1911 Heald and Wolf59 reported from Texas the
Corticium stage of the fungus on carrot. They stated that the roots
were covered by white, ropy strands of the fungus, but that no serious
rotting was observed.
CELERY, Apium graveolens
A damping-off of celery seedlings in flats by RMzoctonia Solani has
been observed in the Station vegetable-gardening greenhouses. The
symptoms are similar to those described for beets.
During a search in the market in the winter of 1914 for leaf spot
and soft rot on celery, several bunches shipped from New York were
1916] PARASITIC BHIZOCTONIAS IN AMERICA 321
found to have a brown mycelium and many small sclerotia between the
stalks near the base. The fungus was causing no injury to the celery.
When examined in the laboratory, the mycelium and sclerotia proved
to be those of Rhizoctonia. Pure cultures of the fungus were obtained
readily from the sclerotia. Repeated examinations of new shipments
of celery from New York showed that in the majority of cases Rhizoc-
tonia was present between the stalks.
Duggar and Stewart32 in 1901 were the first to report Rhizoctonia
causing a destructive damping-off of celery seedlings. Rolfs95 in 1905
reported a damping-off of seedlings in Florida caused by Corticium
vagum B. & C. Van Hook136 found a Rhizoctonia associated with a
root rot of celery in the field. He did not believe, however, that this
fungus was the cause of all the trouble. Affected plants never attained
full size, and an examination of the roots showed considerable decay.
The disease seemed to affect the main roots, which rotted off rapidly
near the crown. The fact that seed beds in new soil did not entirely
control the trouble showed that the fungus Rhizoctonia was present in
the new soil, tho not in any great amounts. Halligan,51 in Michigan,
has also studied the damping-off of celery plants in the seed bed.
Centaurea gymnocarpa
In the spring of 1914 a large number of seedlings of Centaurea
gymnocarpa, including some of those which were potted, damped off.
By June many of the potted plants were dying with stem rot, the dis-
ease having been carried over on affected seedlings and in a few cases,
no doubt, on healthy ones. Microscopic examination and pure cultures
showed that in each case R. Solani was present in the diseased tissues.
The progress of the disease was rather typical. The first symptom
was the wilting and drying up of the foliage. On pulling up the
plant, a number of the leaves were seen to be rotted off at the crown,
while the bark on the stem below the surface of the ground sloughed
off and the tissues beneath were wet and stringy.
CLOVER, RED, Trifolium pratense
In the spring of 1914 damping-off of red and Japanese clover was
observed in the agronomy greenhouses. A culture easily obtained
from the fungus appeared to be the same in all respects as the one
isolated from alfalfa seedlings which were growing under similar con-
ditions in close proximity.
Stevens and Wilson 122 in 1911 reported that in a field of clover in
North Carolina the roots were being attacked by Rhizoctonia and were
suffering some damage. This is the only instance in which Rhizoctonia
has been reported as injuring clover in the field.
322 BULLETIN No. 189 [June,
COLEUS, Coleus sp.
In November, 1912, cuttings of coleus began to damp off in a bench
in the floricultural greenhouses. The variegated green varieties seemed
more susceptible to the fungus than the variegated red and yellow. The
trouble was found to be due to R. Solani. The infected cuttings showed
characteristic lesions on the stems at the surface of the sand. These
lesions were quite large and distinct, brown in color, and depressed
several millimeters at the center. They were generally found on one
side, but in some cases the whole cutting was girdled. Practically all
the coleus cuttings in the bench damped off in this manner.
During October, 1913, Ehizoctonia was found causing a damping-
off of coleus seedlings planted very close in flats. About half the plants
damped off.
Duggar and Stewart32 reported a damping-off of coleus cuttings
in New York, caused by Rhizoctonia, similar to that observed at this
Station.
CONIFEROUS SEEDLINGS
The first case reported of damping-off of white-pine seedlings due
to Rhizoctonia was by Duggar and Stewart,32 from New York. Ten
years later Clinton1 7 mentioned the damping-off of a number of conif-
erous seedlings.
Hartley,55 who made a study of the damping-off of coniferous seed-
lings in the West, found that Rhizoctonia is one of several organisms
involved. He wrote as follows :
"Ehizoctonia (probably Corticium vagum B. & C.), which causes dumping-off
of very young seedlings, sometimes continues to work in patches till the plants are
two months old or even more. On sandy soil, when seedlings from five to nine
weeks old are killed, the youngest and deepest parts of the roots are usually first
attacked. At Halsey, roots of Eocky Mountain yellow-pine seedlings about seven
weeks old have been attacked at points as much as eleven inches below the ground
surface. In many plants as old as this the older parts of the roots resist the en-
trance of the fungus which has rotted the younger parts and throw out new root
branches, so that recovery takes place without any evidence of the damage being
shown by the plant above ground. ' '
Coreopsis lanceolata
Duggar and Stewart32 in 1901 mentioned the fact that next to a
plot of sweet williams that were being killed by Rhizoctonia, were two
rows of Coreopsis lanceolata which were also diseased. They stated
that "only a few plants were killed, but from many of them the lower
leaves had rotted away. The rot seemed to start in the base of the
petiole, where it came in contact with the soil. The decaying leaves
were overrun with Rhizoctonia."
1'AKAsiTK' BHIZOCTOMIAS IN AMERICA
323
CORN,' Zea mays
In 1914, during the progress of the soil survey for R. Solani, the
fungus was found frequently on corn roots in the field. It could not
be determined whether the fungus penetrated the roots or not, but
there was no question as to the abundance of the mycelium on the
roots.
Rolfs05 in 1905 reported Corticium vagum B. & C. on corn in
Florida.
COTTON, Gossypium herbacsum
Grlover40 in 1855 described a
respects is the same as the disease
FIG. 13. — STEMS OF YOUNG CARNA-
TION PLANTS INOCULATED WITH
EHIZOCTONIA FROM COTTON,
SHOWING LESIONS CHARACTERIS-
TIC OF SORE SHIN OF COTTON
CAUSED BY THE SAME FUNGUS
sore shin of cotton, which in some
of seedling cotton caused by Rhizoc-
tonia. He stated that ' ' the cause is
attributed by many to cold, cutting
winds, when the plant is very
young. Others, however, assert that
when a high wind shakes a tender
plant, the main stem is so much
bent and twisted that the sap ves-
sels are upturned and a serious in-
jury occurs."
One of the causes of sore-shin
disease of cotton remained undis-
covered until Atkinson,5 in 1896,
found in the diseased tissues a ster-
ile mycelium, which he later identi-
fied as Rhizoctonia. By means of
pure-culture methods and inocula-
tion experiments he further proved
that this sterile fungus was the
cause of sore shin and also of seed-
ling rot and damping-off of cotton.
He describes the Rhizoctonia dis-
ease of cotton as follows :
' ' There are several phases of the disease. Sometimes the tissues undergo a
soft rot which progresses very rapidly, and the early stages are not marked by any
striking color characteristics. Another phase may progress rapidly or slowly and
is usually quite well characterized by a reddish brown color which accompanies it.
This phase is also characteristic in that it is usually manifested on one side of
the stem in the form of an ulcer which gradually deepens until the vascular sys-
tem is reached, when the life of the plant becomes really endangered. Even when
this stage is reached, however, the plant may, and does frequently, recover.
"This latter phase is characteristic of a very common disease of seedling
cotton. It is called by the planters in many places ' sore shin. '
"The diseased portion of the plant is just beneath the surface of the ground
and presents an area of shrunken tissue of a dull brown or reddish color. The
324 BULLETIN No. 189 [June,
size of the shrunken area and the depth of the injury are proportionate to the
serious condition of the ulcer, as it may be termed. If the injury remains con-
fined to the superficial tissues, the plant will usually recover. It does sometimes
recover when the injury reaches the vascular tissue, but more frequently death
results when the trouble has progressed thus far. ' '
No further original work has been done on this disease since the
time of Atkinson, altho several of the southern experiment stations
have published bulletins on cotton diseases, including the sore shin
and seedling rot due to Rhizoctonia.
DiantJius
R. Solani was isolated from diseased plants of DiantJius barbatus
(Newport Pink), during July, 1913, in the perennial garden of the
Station. This variety and DiawtJius barbatus (single mixed) were
much more susceptible to stem rot than were any of the other varieties
grown. In fact, practically every plant of these two varieties died
from stem rot during the summer. These varieties are more like the
carnation than any of the others, and when affected, the symptoms of
the disease were very similar to those of stem rot of carnation. The
first evidence of the disease was the pale green color of the leaves,
followed in many cases by a sudden wilting of the foliage. When
plants in this stage were pulled up, the bark readily sloughed off,
leaving the wood exposed. When plants in the later stages of the
disease were pulled up, the stem usually broke off at the surface of the
ground, exposing stringy tissue.
During the same month, a disease of DiantJius sequeri and D.
plumarius was under observation. Diseased parts of these plants
yielded Rhizoctonia in every instance. In the case of D. sequeri the
fungus seemed to be living saprophytically among the numerous pros-
trate, bushy branches. The brown strands of the mycelium could be
plainly seen running thru the bushy mass of the plant. Only a few
plants died. Unlike the case of D. barbatus, there was no characteris-
tic sloughing off of the bark, but a more or less general rotting of the
whole stem, which left the tissues very dry and stringy. The attack
was not confined to the main stem, but affected any of the branches
which touched the ground.
Most of the plants of D. plumarius, occupying a space about three
feet long, died from attacks of the fungus. The symptoms of the dis-
ease were very similar to those of D. sequeri, the rotting appearing
to extend gradually from one point thru the whole stem. As with D.
sequeri also, the bushy habit of the plant gave ample protection to the
fungus, and the radiating strands of the brown mycelium of Rhizoc-
tonia were visible to the naked eye.
Duggar and Stewart32 in 1900 found a badly diseased plot of
DiantJius barbatus in which 90 percent of the plants, in the course
of the season, died from stem rot due to Rhizoctonia.
1916] PARASITIC RHIZOCTONIAS IN AMERICA 325
EGGPLANT, Solatium melongena
During August, 1912, while some field observations were being
made on carnation stem rot, the fruits of a number of eggplants in
an adjoining field were found to be rotting at the point where they
touched the ground. The decay spread in all directions from this
point, making a sunken, brown area ; this was followed by the soften-
ing and subsequent collapse of the surrounding tissues. Fruits showing
this decay were brought into the laboratory and placed under a bell
jar. Around the diseased spot there soon developed a thick mass of
mycelium, which on microscopic observation was found to consist of
hyphse of Fusarium and Rhizoctonia. The decaying spots contained
no fungous threads, but were completely filled with bacteria. On plat-
ing, pure cultures of R. Solani were obtained. The cause of the pri-
mary infection is not known. It is very probable that both the Fusar-
ium and Rhizoctonia entered the tissues where the epidermis had been
destroyed.
In July, 1913, the damping-off of a number of eggplant seedlings
in the vegetable greenhouses was noticed. This was shown, by pure
cultures of the diseased material, to be due entirely to Rhizoctonia.
The fungus produced the characteristic lesions on one side of the seed-
lings at the surface of the soil, causing the stem to break.
Atkinson,4 in his account of damping-off diseases, mentioned
eggplant seedlings among those susceptible to attacks of the sterile
fungus (Rhizoctonia). Rolfs95 reported the presence of the Corticium
stage of Rhizoctonia on mature plants in an irrigated garden. Here
the plants affected drooped for a time and then wilted and died. Le-
sions were formed on the stems at the surface of the ground.
Wolf140'141 in 1914 reported damping-off and a fruit rot of eggplants
due to Rhizoctonia (Corticium vagum B. & C.), but he does not re-
gard the fungus as the cause of serious injury to eggplants.
FIVE-FINGER, Potentilla sp.
A number of five-finger plants were found to be infected with
R. Solani during June, 1914, in inoculated sections in the floricul-
tural greenhouses. The mycelium of the fungus was present at the
nodes which touched the soil and also at the bases of the plants, where
crown rot was developing.
FOXTAIL GRASS, Setaria glauca
Several plants of foxtail grass growing under the same conditions
as the preceding host, five-finger, showed a root infection.
GypsopMla repens
A number of Gypsophila repens plants were found diseased in the
herbaceous grounds during July, 1913. Pure cultures of the diseased
326 BULLETIN No. 189 [June,
material showed the causal organism to be R. Solani. The plants were
bushy, so that some of the branches and leaves were in contact with
the soil. The symptoms and appearance of the disease were similar
to those described for Dianthus.
LAMB'S QUARTERS, Clienopodium album
During the summer of 1913 several wilted Clienopodium plants
were observed along the border of the old herbaceous grounds of the
Station. On pulling up the wilted plants, it was found that R. Solani
was the cause of the wilting. The fungus did not enter very deep
into the tissues, but rather girdled the stem and formed a scurfy layer.
Duggar and Stewart32 in. 1901 reported the occurrence of Rhizoc-
tonia on Clienopodium album.
Lavatera arborea variegata
During March, 1913, in the floricultural greenhouses, a number of
seedlings in small seed pans, among which were several pans of Lava-
tera, began to damp off in a manner characteristic of R. Solani.
Pure cultures of diseased seedlings yielded this fungus. Strands of
the brown mycelium could be seen on the surface of the soil and
extending up on the stems and leaves. This was noticed again in the
spring of 1914.
LETTUCE, Lactuca sativa
Atkinson4 in 1895 mentioned the damping-off of seedling lettuce,
among a number of other plants, by a sterile mycelium which later
proved to be Rhizoctonia.
Stone and Smith128 found that R. Solani caused a rot of green-
house lettuce, altho the disease was not common. The first appearance
was on the lower leaves where they lay on the ground ; a brown rot
set in, which spread thru the leaf in a very characteristic manner.
The green blade rapidly rotted away, leaving the midrib and stalk as
sound as tho the blade had been carefully cut away or had been eaten
by insects.
Duggar and Stewart32 observed the damping-off of lettuce seed-
lings by Rhizoctonia for a number of years. They found that at or
near the surface of the ground the tissues become water-soaked in
appearance and unable longer to support the seedling, so that it falls
to the ground, the fungus invading all parts. Within a day or two
this fungus, under favorable conditions, wilted do\vn and destroyed
whole boxes of lettuce seedlings. Duggar and Stewart also observed
several times what was apparently the same fungus causing a disease
of mature lettuce plants. On the older leaves the leaf blades alone
were affected, but the more delicate inner leaves succumbed entirely,
blackening and decaying with the progress of the disease.
1916]
PARASITIC KHIZOCTONTAS IN AMERICA
327
Iii 1903 Selby104 reported the presence of a rosette disease of let-
tuce, which he described as follows: "The plants affected showed,
usually not long after transplanting, but occasionally at other stages,
a failure to send out central leaves freely. The leaf-bearing axis re-
mained shortened, and the last leaves formed remained short, making
a very striking contrast to the remainder of the plants in the bed
and to the lower leaves of the same plant. (Frequently the plants
overcome this tendency and make a fair amount of product with
longer time.) Examination of the roots showed areas occupied by
the hyphae of Rhizoctonia. " In 1906 Selby106 treated at length the
control of rosette in lettuce due to Rhizoctonia.
Fio. 14. — DAMPINO-OFF OF LAVATERA SEEDLINGS BY Bhizoctonia Soldni
(Experiment 9)
328 BULLETIN No. 189 [June,
In 1905 Rolfs05 reported the presence of the perfect stage, Cor-
ticium vagum B. & C., on lettuce from Florida.
Lobelia erinus (Single Blue)
The lobelia plants in the floricultural greenhouses in 1914 were
small and sessile, and covered the tops of the pots in which they were
growing. In June a number of them began to die. On close exami-
nation, strands of R. Solani could be seen spreading thru the mass of
plant material. The low-lying leaves afforded a good hiding place
for sow bugs, and no doubt they helped in carrying the fungus from
one pot to another. Attacks of Rhizoctonia on other varieties of lobelia
have been observed in the greenhouses a number of times.
ONION, Allium sp.
A culture of Rhizoctonia isolated from onion seedlings was ob-
tained from Cornell University by Mr. H. W. Anderson in 1911. Since
that time the author has worked with this strain both in the laboratory
and in the greenhouse. From its morphological and physiological
behavior, it must be classed as distinct from the other strains.
Dr. I. C. Jagger states in a letter that he first isolated this form
from onion on May 29, 1911, from seedlings growing on muck soil in
New York. He found that the Rhizoctonia mycelium was always con-
fined to the first, or seed, leaf and that damping-off ceased as soon as
the second leaves had developed.
PANSY, Viola tricolor
During the fall of 1913 pansy plants were placed in a solid bed,
in the floricultural greenhouse, as a border for sweet peas. At that
time some of the sweet-pea plants died, and eventually a culture of R.
Solani was obtained from them. The following April several pansy
plants in the vicinity of the spot where the sweet peas had died became
diseased and later died. A culture showed the trouble to be due to
Rhizoctonia. Later a large number of the plants in the row died. The
fungus attacked the plant at the crown and caused a rapid rot. The
prostrate branches, the petioles of the leaves, and even the leaves them-
selves were also rotted in a characteristic fashion. The strands of the
mycelium could easily be seen ramifying between the rotting mass
arid the soil.
PLANTAIN, Plantago aristata
Diseased plants of plantain were found during June, 1914, in
inoculated sections in one of the floricultural greenhouses. The
mycelium of R. Solani was present around the bulbous base of the
1916] PARASITIC EHIZOCTONIAS IN AMERICA 329
plants, causing a crown rot. In one or two cases several leaves were
completely rotted at the crown.
POINSETTIA, Euphorbia pulcherrima
About October 7, 1912, young poinsettia plants were taken from
the cold house (50° to 60 °C.) of the flori cultural greenhouses and put
in a box with a glass top. They were then placed near the cutting
bench, in which a number of plants of various kinds were damping off.
The poinsettia cuttings shortly afterwards began to die off rapidly.
The characteristic lesions on the stems of the young plants and pure
cultures of the diseased material indicated that this condition was due
to R. Solani. The lesions, instead of being on one side and more
or less localized, in almost every case formed a collar around the stem
at the surface of the soil. The collar was about 2 to 3 millimeters
wide, somewhat depressed, and of a dark color. Strands of the brown
mycelium were visible spreading over the soil in the pots. This infec-
tion probably had its origin in the cutting bench.
POTATO, Solanum tuberosum
On the potato R. Solani exhibits a number of interesting charac-
teristics, which vary with climatic conditions, age of the host, and part
of the plant attacked.
The sclerotial stage of this fungus has been observed on practically
every Illinois potato tuber examined by the writer. Moreover, in
every shipment from other states which has been examined, the fun-
gus has been found present. The tubers affected were dotted with
brownish black sclerotia of various shapes and sizes (Fig. 15), but so
far as could be determined, they were causing no direct injury. This
type of Rhizoctonia disease of potato is the one most commonly found
in the United States.
R. Solani also causes, under certain conditions, a russeting, or
scab, a cracking of the tuber, the formation of pits at or near the len-
ticels, and a wet rot of the tuber. These types of injury have been ob-
served by Rolfs92'93 in Colorado, by Orton73 in various states, and
by Morse and Shapovalov69 in Maine.
On the plant itself this fungus produces various types of diseases.
In many cases young plants are completely cut off before they reach
the surface of the ground. Older plants that are severely attacked
just below the surface of the ground usually die off quickly. If they
are only slightly attacked, the fungus produces small lesions on the
stems, the plants take on a dwarfed and unhealthy appearance, and
the tubers remain small, altho the plants usually live thru the sum-
mer. When the stem is girdled by the fungus so as to prevent trans-
location entirely, large tops are produced, aerial tubers are formed,
330
BULLETIN No. 1SU
FIG. 15. — POTATO TUBER SHOWING THE SCLERGTIA. OF Rhizoctonia Solani
J.016] PARASITIC EUIZIHTONJAS IN AMKKICA 331
and in some cases a curling of the leaves or resetting results. When
the main stein is attacked below the surface of the soil and the stolons
are cut off, the condition known as "little potatoes" is produced; in
such cases a cluster of small, short-stemmed tubers is formed above
the wound. The production of aerial potatoes, rosette, and leaf curl-
ing also occurs when the stolons are attacked and the young tubers arc
cut off.
These abnormal developments of the potato are usually associated,
and are secondary physiological effects due to disturbances of the
nutrition of the plant. They occur most frequently on poorly drained
land and especially on heavy soils.
Rolfs92 attributed the potato failure of 1902-03 in Colorado to
little potato. Selby103 in Ohio, in his studies of the Rhizoctonia dis-
ease on potato, gave particular attention to rosette. In 1914 Morse
and Shapovalov09 concluded that the Rhizoctonia disease of potato is
of a more serious nature than is generally considered. In one field
which they had under observation for several seasons, they attributed
the poor and uneven stands, unexpected low yields, early ripening,
and death of the tops to Rhizoctonia. In most cases they confirmed
the observations made by Rolfs. Recently investigators all over the
country have been emphasizing the serious nature of the disease.
In January, 1915, material of Rhizoctonia Crocorum on potato
tubers was received from Mr. F. D. Bailey of the Oregon Agricultural
Experiment Station. On comparing it with Rhizoctonia Solani, it was
found to be entirely different in all respects. However, this fungus is
identical with the fungus on alfalfa reported by a number of observers
(Webber, Heald, and Freeman) as R. Crocorum. Thus it appears
that R. Crocorum is present in this country on alfalfa and on potato
tubers.
Bailey8 describes the Rhizoctonia disease of potato as follows :
' ' The surface was almost entirely covered with a dense, felt-like mat of a
chocolate color when dry, violet -brown when moist. This mat was found to be
composed of mycelium which had long narrow cells and a branching habit char-
acteristic of Rhizoctonia. The greater part of this mycelial mat could be easily
removed, and beneath this the surface of the tuber was covered with very small
dark spots. These spots appeared to the unaided eye as minute eruptions of the
skin. Under the microscope one can see the mycelial threads attached at these
points, and a freehand section thru such a spot shows it to be a structure com-
posed entirely of interwoven fungus threads forming a sclerotium. No evidence of
differentiation or any type of spore formation within this body could be found
on examination of many sections. The portion of the sclerotium near the sur-
face is composed of cells that are very deeply colored, giving the black appear-
ance. The outer surface of the sclerotium is seen to project above the surface,
while the lower or underlying portion is embedded in the outer cortical layers
of cells of the tuber. Furthermore, there is a strand of fungus tissue extending
deeper than the sclerotium, which connects it with a layer of the same type of
fungus tissue spreading between the cortex and parenchyma from the poini where
this strand reaches the parenchyma.
"Attempts to grow this fungus in culture failed. This has been the experience
reported in attempts to grow Khisoctonia violacea Tul. "
332
BULLETIN No. 189
RADISH, Eaphanus sativus
[June,
Damping-off of radish seedlings by R. Solani has appeared sev-
eral times in the floricultural greenhouses. During May, 1914, an at-
tack of Rhizoctonia on mature radishes was observed in the writer's
home garden. The first sign of the disease was the yellowing of the
foliage, followed by the wilting of the leaves. On pulling up a
plant, the crown was found to be rotted at the base of the leaves. The
rot progressed slowly and killed only a few of the plants. After it
had proceeded for some length, the radishes cracked farther down.
This is very characteristic of the disease at this stage (Fig. 16).
In 1895 the damping-off of radish seedlings by a sterile fungus,
which was later identified as Rhizoctonia, was first reported by Atkin-
son.4 Duggar and Stewart32 in 1901 noted a disease caused by Rhi-
zoctonia of mature radishes forced in a greenhouse. The disease
caused a soft rot of the crown or lesions in this region. The leaves
were generally unaffected until a large part of the root had decayed.
Plants in all stages of growth were affected and killed. Duggar and
Stewart also found a Rhizoctonia in connection with the damping-off
of radish seedlings in the greenhouse.
FIG. 16. — LATE STAGE OF ROOT EOT OF RADISHES CAUSED BY Rhizoctonia Solani
1916] PARASITIC RHIZOOTOXTAS IN AMERICA 333
In 1904 Clinton14 observed a damping-off and root rot of radish
due to Rhizoctonia. Apparently the disease was not very serious.
Stewart125 in 1910 also reported a damping-off and root rot of radish
due to Ehizoctonia. Infection took place first at the level of the soil,
causing the leaves to have a wilted, drooping appearance. From this
point the disease spread into the leaves and roots of the plant, soon
causing death. On mature radishes, decayed spots of irregular shape
were produced, and at an advanced stage the diseased portions of the
plant were covered with a white, felted mycelium.
RHUBARB, Rheum rhaponticum
In 1901 Duggar and Stewart32 reported a disease of rhubarb, on
Long Island, which they had had under observation for several years.
They described the disease as follows :
' ' An unthrifty condition of the plants was noticed, followed by the rapid
dying off of many of the leaves. The affected leaves became dry and shrunken
in appearance and soon fell to the ground. Where a field was badly affected,
the majority of hills showed the trouble to the extent of at least a leaf or two.
In several instances from one-fourth to three-fourths of the leaves were already
dead. An affected leaf breaks off readily just beneath the surface of the ground,
and old dead leaves rotted off in this region. The general appearance reminded
one strongly of the effect of Rhizoctonia upon beets. There was very little super-
ficial mycelium visible to the unaided eye. Microscopic examination showed
hyphse of a Rhizoctonia both superficially and immediately under the surface where
the leaves were rotting."
Clinton14 has also reported a stem rot of rhubarb due to Rhizoc-
tonia. He found the fungus at the base of leaf petioles, causing dark,
sunken cankers.
SALVIA, Salvia splendens
The symptoms of the Rhizoctonia disease of salvia observed in the
flori cultural greenhouses were similar to those described for coleus.
All varieties of the cuttings in the bench seemed to be equally suscep-
tible. It has been shown that the serious damping-off of the salvia, al-
ternanthera, and coleus was due to the fungus which was first brought
in on the mature alternanthera plants from which cuttings were made.
(See Alternanthera, page 310.)
Santolina chamcecyparissus
In 1914 a number of plants of Santolina chamcecyparissus growing
in pots next to the Centaurea gymnocarpa in the floricultural green-
houses, were found to have a typical stem rot, due to R. Solani, very
similar to the disease as described for that plant (see page 321). The
fungus could be distinctly seen running thru the bushy branches.
334 BULLETIN No. 189 [June,
Sedum sp.
A few plants of Sedum anglicum, together with several other spe-
cies of Sedum, were found diseased, in July, 1913, in the herbaceous
grounds. The progress of the disease was very slow ; few plants were
killed during the entire summer. For the most part, the fungus
seemed to live saprophytically at the base of the plant. It was also
found on healthy plants of this genus.. About six species were planted
in a row in the garden, and all were affected in much the same way.
SORREL, Rumex acetosella
In June, 1914, a number of sorrel plants were found diseased in
an inoculated section in the greenhouse. The stems of the plants were
covered with the brown strands of mycelium, and a few of the leaves
were rotted off at the crown. Pure cultures of the diseased parts
yielded R. Solani in every case.
During July, 1912, when the young sweet peas in the field were
about one-third to one-half grown, occasional vines showed evidence
of disease by turning yellowish, wilting, and finally drying up en-
tirely. An examination of the affected plants showed that they were
more or less separated from their roots near the surface of the ground.
Pure cultures of the diseased material yielded R. Solani in all cases.
In November, 1913, several diseased seedlings were brought in from
the plant-breeding greenhouses. On close examination the stems
showed the characteristic lesions caused by Rhizoctonia. The same
trouble occurred in the floricultural greenhouses the past two seasons,
but in no case was it severe.
During the winter of 1913, the writer was called to Chicago to look
over a range of greenhouses devoted to the growing of sweet peas.
Sweet-pea plants of all ages were seriously affected. Dead plants were
scattered thru the whole house. Close examination of the diseased
plants revealed the fact that Rhizoctonia was causing the trouble.
Apparently it started in the seed pans and continued to work until the
plants were ready to be discarded. The symptoms in each case were
the same — yellowing of the foliage, followed by the wilting and dry-
ing up of the plants. Characteristic lesions, which finally cut the
stems off at the surface of the soil, could always be found on the dis-
eased plants. The root systems were much dwarfed.
In 1908 Clinton16 observed in Connecticut a damping-off of sweet
peas due to Rhizoctonia. Taubenhaus130'131 in describing a Rhizoc-
tonia rot of sweet pea at different stages, states that he found it quite
destructive to the plants when they are in the seedling stage.
I'AHA.SITIC RimCKTOXlAS IX AMERICA 335
TOBACCO, Nicotiana sp.
In 1904 Clinton14 noticed a seed-bed rot of tobacco, which he
thought was due to Rhizoctonia. The same year Selby105 observed a
similar bed rot of tobacco in Ohio caused by Rhizoctonia. He stated
that the specific characteristics of the fungus do not differ essentially
from those of its forms on other plants, including potato.
Clinton,15 in making another report on this disease, in 1906, stated
that the injury to the plants was slight and was confined, as with the
potato, to the underground parts.
Johnson63 has carried on some extensive work on Rhizoctonia, with
a view to controlling the damping-off of tobacco seedling^.
TOMATO, Lycopersicum esculentum
A damping-off disease of tomatoes caused by Rhizoctonia has been
noted from a number of states; the symptoms of the disease are the
same as have been described for a number of other plants, such as
eggplant.
In connection with his wrork 011 the potato rosette resulting from
Rhizoctonia, Selby104 also mentioned a tomato rosette caused by the
same fungus. He stated that the tips of diseased plants showed
rather long internodes and dwarfed leaves, with somewhat curled-leaf
aspects, while the roots had lesions and other similar features found
in potato rosette.
. Rolfs95 in 1905 stated that he frequently found the Corticium stage
on the tomato plant, but that apparently the plants do not suffer ma-
terially from its presence when planted on well-aerated land. He
described it as follows :
"The fruiting stage of the fungus develops freely on the stem just above the
surface of the ground, often extending up the stem for a distance of six inches.
As a rule the fungus does not penetrate the tissue here, but simply covers the stem
of the plant. The tomatoes which touch the ground are frequently more or less
covered by a fruiting membrane of the fungus, which mars the appearance of the
ripe fruit. So long as the tomatoes are green and the skin uninjured, the fruit
remains sound ; however, if the skin is ruptured, the fungus soon destroys it, pro-
ducing a brown rot. This organism also frequently gains entrance to the fruit at
the stem end."
Orton72 described the rosette of tomato caused by Corticium vagum
B. & C. as a disease of minor importance in tomato culture. He stated
that ' ' the fungus attacks the roots and base of the stem, forming dark
cankers. The effect on the plant is to dwarf and curl the leaves and
to restrict productiveness."
A fruit rot of the tomato has also been observed by Pool86 and
again by Wolf.141 Pool described the symptoms of the fruit rot as
follows :
' ' The specimen examined showed no rupture in the external skin visible to
the naked eye. The diseased area was plainly distinguishable by the chocolate-
336 BULLETIN No. 189 [June,
colored, slightly wrinkled epidermis. An examination of the underlying tissues
revealed the same general color and numerous, somewhat darkened filaments pene-
trating the cells in all directions."
Wollenweber1 42 in 1913 described a species, Rhizoctonia poto-
macensis Wr., which causes a fruit rot of green tomatoes. He stated
that this species differs from Rhizoctonia Solani in the character of
its attacks, in that concentric, subepidermal mycelial zones are formed
within the tomatoes.
VIOLET, Viola odorata
During ^he fall of 1913 a number of violet plants in the floricul-
tural greenhouses were found to be diseased. A few had stem rot,
while on others only the bases of the petioles were somewhat rotted.
Where the pots were set close together and the plants overlapped, the
brown strands of R. Solani could be plainly seen spreading out from
one plant to another. However, in no case was the disease severe ; it
is probable that the fungus was living saprophytically on the lower
leaves.
Duggar and Stewart32 observed, in a greenhouse in New York, one
case of destructive violet stem rot due to Rhizoctonia and a second
case similar to the attack described above.
ADDITIONAL OBSERVATIONS
Beside the hosts that have been mentioned, observations have been
made in the floricultural greenhouses of diseased seedlings and cut-
tings of a number of other plants, tho no work has been done further
than to make a microscopic examination of the diseased material.
Below is a list of seedlings and cuttings found damping off in the
spring and fall of 1914, with the percentage of loss resulting. In all
cases Rhizoctonia proved to be the cause of the trouble.
Percentage
Seedlings Damping off, April 6, 1914 of loss
Amaranthus caudatus 75
salicifolius 90
Bartonia aurea 90
Calendula Pongei 1-2
Celosia Huttoni, var. Thompsonii magnifica 75
Chrysanthemum hortorum 30-40
Dianthus chinensis 80
Heddewigii 30
latifolius 80
Godetia sp 80
Gypsophila muralis 30
Kochia trichophylla 99
Lavatera arborea variegata 5
Linaria Maroccana 5
Linum grandiflorum rubrum 30
Lychnis coeli rosa 90
Portulaca oleracea 80
Schisanthus sp 2-4
1916] PARASITIC EHIZOCTONIAS IN AMERICA 337
Percentage
Seedlings Damping off, September 2, 1914 of loss
Aqullegia (6 species) 85
Campanula (8 species) 80
Cineraria (several species) 20
Dianthus plumarius 85
Erysimum pulchellum 2
Linaria Cyinbalaria 2
Lythrum sp 2
Matthiola incana (stocks) 2
Primula malacoides 2
' ' obconica grandiflora 2
Schizanthus (mixed) 2
Kilene Schafta 100
Stachys lanata 2
Viola tricolor (3 varieties) 20
Cuttings Damping off, September 25, 1914
Abutilon hybridv/m, var. Savitzii 100
Acalypha Wilkesiana, var. bicolor 100
tricolor 100
" " marginata 90
Ageratum mexicanum vars 2
Alyssum odoratum (3 varieties) 100
Coleus (10 varieties) 2
Cuphea platycentra 2
Iresine (Achyranthes) (5 varieties) 95
Petunia (several varieties) 100
Piqueria trinervia (Stevia) 100
Santolina chamcecyparissus 2
Sedum spectabile 2
Telanthera (Alternanthera) (9 varieties) 2
Vinca major (several varieties) 2
TYPES OF SYMPTOMS
From a study of the symptoms caused by Rhizoctonia Solani on
the various hosts, it is seen that, except for a few minor points, they
are the same when appearing on the same type of host. The damping-
off of seedlings and cuttings of various plants is identical, as is the
rotting of a number of root crops. In most herbaceous plants a stem
rot is produced, the symptoms of which are also identical on the vari-
ous hosts. On very resistant plants lesions only are formed ; these are
apparently identical on the different hosts.
INOCULATION EXPERIMENTS
The main purpose of these inoculation experiments was to ascer-
tain the degree of biologic specialization which may exist between the
various cultural strains of Rhizoctonia, or between strains isolated
from different hosts or of different geographical origin. With three
thousand square feet of glass available in the floricultural greenhouses
and with the assistance of the members of the floricultural division, it
was possible to carry on cross-inoculation experiments involving about
338 BULLETIN No. 189 [June,
3,000 cuttings, 2,000 plants, and 7,000 seedlings of various kinds. With
these, comparisons were made of about forty-five strains of Rhizoctonia.
A large number of the strains used in these experiments were iso-
lated by the writer from the various hosts found infected with Rhizoc-
tonia in this vicinity. Other strains were obtained from various in-
vestigators thruout the country. Below is presented a list of the strains
used and the source of each.
Alfalfa. — A Rhizoctonia culture from alfalfa was received from Dr. C. W.
Edgerton, Baton Rouge, Louisiana, November 12, 1912. It was originally ob-
tained by Dr. Edgerton in May, 1910, from alfalfa seedlings.
Alternanthera B.A.C. — -A. culture of Rhizoctonia was isolated from infected
alternanthera cuttings found in the floricultural greenhouses in the fall of 1912.
Alternanthera R.A.F. — This strain was obtained at the same time as the
preceding, from mature alternanthera plants in the field.
Amaranthus. — In August, 1913, Mr. W. H. Burkholder, of Cornell University,
contributed several specimens of AinarantTws retroflexus infected with Rhizoc-
tonia, from Irving, New York. The stems were covered with the immature, gray,
felt-like mycelium of the Corticium stage. Scrapings of the hymenial layer of
this stage yielded pure cultures of Rhizoctonia in every case.
Aster. — Early in 1913, Dr. F. A. Wolf sent to the writer a culture of Rhizoc-
tonia which was the cause of the damping-off of China aster seedlings in flats
in the greenhouse at Auburn, Alabama.
Bean. — A transfer of a culture of Rhizoctonia from bean was obtained in
December, 1912, from Dr. J. T. Barrett, of this university. He in turn had re-
ceived it from Dr. M. F. Barrus, of Cornell University, about 1910.
Beet. — A culture of Rhizoctonia was obtained from young seedlings of the
garden beet found damping off in the vegetable-gardening greenhouses, July 10.
1913.
Begonia. — The strain from begonia was isolated by Mr. Anderson from cut-
tings found damping off in the floricultural greenhouses in the fall of 1911.
Carnation. — During the season of 1911-12, Mr. Anderson isolated Rhizoctonia
from a number of carnation plants received from different sources, and during
1912-13 and 1913-14 the work was continued by the author, so that a comparison
of a large number of cultures from diseased plants obtained from various localities
was possible. The strains used are given below.
"Carnation R.K. ": Isolated by Mr. Anderson from diseased carnation
plants obtained at Urbana, Illinois, in October, 1911.
"Carnation R.O. ": Culture isolated by Mr. Anderson in the fall of 1911,
at Urbana.
"Carnation R.H. ": Culture isolated from a diseased plant in the floricul-
tural greenhouses in the fall of 1911 by Mr. Anderson.
"Carnation R.S. ": Isolated from diseased plants received from Kankakee,
Illinois, by Mr. Anderson, October 25, 1911.
"Carnation R. 2": Culture reisolated by Mr. Anderson from infected cut-
tings in sterilized soil in the spring of 1912.
"Carnation R.F. ": Isolated from diseased carnation plants gathered in the
field in the horticultural grounds, July 24, 1912.
"Carnation R.M.2": Isolated from a White Enchantress plant in one of
the floricultural greenhouses during September, 1912.
' ' Carnation R. 107 ' ' : Obtained from a plant in the floricultural greenhouses,
September 7, 1912.
"Carnation R.F.2": Culture obtained from a diseased plant in the field
during the summer of 1913.
"Carnation R. 121-5": A reisolation of Rhizoctonia was obtained on De-
cember 3, 1912, from a diseased plant in one of the inoculated sections of tho
greenhouse.
Carrot. — The strain of Rhizoctonia from carrot used in this work was ob-
tained by Mr. Anderson from Cornell University in 1911. Nothing is known of
the origin of the culture.
1916] PARASITIC RHIZOCTONIAS ix AMERICA 339
Cauliflower. — A culture of Rhizoetonia from cauliflower was obtained in 1912,
from Dr. C. W. Edgerton, Baton Bouge, Louisiana. This culture was isolated
from diseased cauliflower seedlings in the summer of 1912, so that it was a
comparatively fresh culture when received here.
Clienopodium. — A culture was isolated during the summer of 1913 from ma-
ture plants of Chenopodium album growing along the border of the old herbaceous
grounds back of the floricultur,al greenhouses.
Clover. — A culture of Rhizoctonia from red-clover roots was received from
Mr. E. A. Arzberger, Wooster, Ohio, March 3, 1913. The fungus was isolated
by him from red-clover roots in the greenhouse in December, 1912.
Coleus I. — This strain was obtained from coleus cuttings found damping off
in the floricultural greenhouses, November, 1912.
Coleus II. — A culture was isolated from coleus seedlings damping off in seed
pans, October, 1913, in the floricultural greenhouses.
Corn. — The strain from corn was obtained from Dr. J. J. Taubenhaus, New-
ark, Delaware, in 1912. He stated that the fungus had been isolated from corn
seedlings that were damping off in the greenhouse.
Cotton. — Three cultures of Rhizoctonia from cotton received from two
sources at different times, were used in these experiments. The strain ' ' Cotton I ' '
was received from Dr. C. W. Edgerton, Baton Rouge, Louisiana, November 12,
1912. This strain was cultured by him in September, 1911, from young diseased
plants. The strain ' ' Cotton II ' ' was also received from Dr. Edgerton. This
strain was cultured in February, 1912, from the same kind of material as the
above. The third strain, "Cotton III," was received from Dr. F. C. Wolf,
Auburn, Alabama, December 12, 1912. The fungus was isolated from seedling
cotton plants growing in the station greenhouse at Auburn.
Dlanthus. — Cultures of Rhizoctonia were isolated during July, 1913, from
diseased plants of several species of Dianthus growing in the perennial garden.
The strains cultured and used in the experiments were ' ' D. b'arbatus N. P., " " D.
barbatus S. M., " " D. plumarius, ' ' and ' ' D. sequeri. ' '
Eggplant. — Two strains of Rhizoctonia were isolated from eggplant: one,
causing a fruit rot, was cultured August, 1912 ; the other was isolated from seed-
lings damping off in flats in the vegetable-gardening greenhouse, July, 1913.
Gypsophila repens. — A culture of Rhizoctonia was isolated during July, 1913,
from diseased Gypsophila plants in the perennial garden.
Lavatera. — A culture was isolated in 1913 from seedlings of lavatera found
damping off in pans in the floricultural greenhouses.
Lettuce. — The strain from lettuce was obtained by Mr. Anderson in 1911,
from Cornell University.
Poinsettia. — Cultures were obtained from damping-off poinsettia cuttings
found in the floricultural greenhouses, October, 1912.
Potato. — Several strains from potato were used in these experiments. Two
of these strains were obtained from scrapings o-f the hymenial layer of the Corti-
cium stage.
"Potato R.P.C. " — A culture of this strain was isolated from fresh potato
stems received from Dr. I. C. Jagger, Williamson, New York, September 2, 1912.
This material contained the perfect stage, Corticium vagum B. & C. Pure cul-
tures of Rhizoctonia were obtained from scrapings of the hymenial layer.
"Potato R.P.I." — In response to a letter from Mr. Anderson, Dr. Geo. H.
Pethybridge, Clifden county, Galway, Ireland, sent a small box of potato stems
containing the perfect stage, Corticium vagum B. & C. This material was sent by
post, July 18, 1912, and received August 5. A pure culture of Rhizoctonia was
obtained from scrapings of the gray mycelium of the Corticium stage.
' ' Potato R.P.O. ' ' — A culture from potato was obtained by Mr. Anderson
from Cornell University. The strain was old and grew very poorly on agar.
"Potato R. Sol." — This strain, like the preceding one, was obtained by Mr.
Anderson from Cornell University. It also grew very poorly on agar.
Eadish. — A culture of Rhizoctonia from radish was obtained from Cornell
University, by Mr. Anderson, in 1911. This form was very old and probably had
been in culture several years. It was lost in April, 1913.
340
BULLETIN No. 189
[June,
Salvia. — The strain from salvia was isolated from cuttings which were found
in the same bench with a number of other cuttings damping off, October, 1912.
Sedum. — A culture of Ehizoctonia from sedum was isolated from diseased
plants found in the herbaceous grounds in July, 1913.
Sugar Cane. — A culture of Ehizoctonia isolated from sugar cane was re-
ceived from Dr. C. W. Edgerton, November 12, 1912. This culture was obtained
in April, 1912. It was fresh and virulent.
Thistle. — A culture of Ehizoctonia from thistle was obtained by Mr. Ander-
son from Cornell University in 1911.
The method of infecting the cuttings, seedlings, and young plants
grown in flats and benches, was as follows : Small flats, varying in size
with the experiment, were first soaked in a strong solution of formalin
for several minutes and then allowed to dry. Steam-sterilized sand
or soil and a soil culture of Rhi-
zoctonia were then mixed to-
gether in the flats and watered.
After being tamped down, the
flats were left standing for two
days in order to allow the fun-
gus to spread thru the soil.
Later, the cuttings, seeds, or
plants were put in the flats and
placed in a, chamber in the green-
house where the moisture could
be controlled. Bottom heat was
furnished. The temperature var-
ied somewhat during the experi-
ment, but the average was about
60° F. When only individual
plants in pots or in benches were
to be infected, a portion of a cul-
ture of Rhizoctonia two weeks
old on green-bean plugs was
placed in contact with the stem
of each plant about one-half
inch below the surface of the soil,
where it would be protected from
light and desiccation.
In obtaining soil cultures of
Rhizoctonia in large quantities.
Mason jars with modified covers
were found to be very suitable
containers. A hole about one
inch in diameter was cut in the
FIG.
17. — SOIL CULTURE
KHIZOCTONIA
OF
1916] PARASITIC BHIZOCTONIAS IN AMERICA 341
center of the cover, and a small tin tube about two inches long was in-
serted and soldered in. This hole was plugged with cotton. (See
Fig. 17.) A mixture of 200 grams of dry sand and 10 grams of corn
meal was then placed in the jars and moistened with distilled water
until the sand was wet thru. The jars and their contents were then
sterilized for one hour at twenty pounds pressure in an autoclave, after
which the sand was inoculated with a small piece of infected green-
bean plug upon which Khizoctonia was growing luxuriantly. In about
a month the soil was permeated with the mycelium, and numerous
brown sclerotia of various sizes were formed. When smaller amounts
of infected soil were needed, a 250-cc. flask was used.
No plant was listed as diseased until a pure culture of Rhizoctonia
had been isolated from it. Pure cultures were easily obtained by soak-
ing small pieces of diseased parts in 1-1000 mercuric chlorid for two
minutes and then placing them on green-bean agar. Rhizoctonia
developed rapidly, and in twenty-four to forty-eight hours would
spread out from the diseased parts.
EXPERIMENTS 1 AND IA: INOCULATION OF CARNATION CUTTINGS WITH
VARIOUS STRAINS OF RHIZOCTONIA
Rhizoctonia is the fungus most commonly found causing a damp-
ing-off of carnation cuttings in the greenhouse. To determine whether
any of the strains from sources other than carnation are able to attack
carnation cuttings with the same ease as those from carnation, the fol-
lowing experiment was carried out. Nine hundred carnation cuttings
and 28 strains were used in 1913, and 1,725 cuttings and 34 strains
in 1914.
Sterilized flats (7x10 inches) were filled with sterilized sand; a
250-cc. soil culture of Rhizoctonia was then added to each and the
sand tamped down and watered. One flat was left uninoculated to
serve as a check. After two days, thirty carnation cuttings (White
Enchantress) were planted in each flat, January 2-3, 1913. The flats
were then placed in the moist chamber.
The inoculated cuttings began to die in about three weeks (Jan-
uary 25), and continued dying until the healthy cuttings had rooted,
when the experiment was discontinued (February 11) (Fig. 18). The
results are given in Table 3.
In most cases the cuttings inoculated with the various strains from
carnation showed a soft, wet, progressive rot at the callus, which
extended in many cases to the surface of the sand. This rot was very
characteristic of the attacks of the carnation strains (Fig. 12). At
other times the fungus attacked the cuttings just below the surface
of the soil, forming lesions of various sizes at the leaf bases. Myce-
lium and sclerotia were also formed along the stems and in practically
all cases between the leaves just above the soil.
342
BULLETIN No. ISO
[June,
TABLE 3. — SUSCEPTIBILITY OF CARNATION CUTTINGS TO VARIOUS STRAINS OF
EHIZOCTONIA: EXPERIMENTS 1 AND IA
Strain
Date of
isolation
Number of plants
Experiment 1: 1913
Experiment la: 1914
Healthy) Wilted
Dead
Healthy
Wilted
Dead
Alfalfa
1910
1912
1912
1913
1913
a
. 1913
1911
1911
1911
1911
1911
1912
1912
1912
1912
1913
a
1912
1913
1912
1912
1913
1912
1911
1912
1912
1913
1913
1913
1913
1912
1913
1913
a
1912
1912
1912
a
a
1912
1913
1912
a
10
2
3
8
'6
3
19
6
5
0
0
1
2
4
0
0
'6
0
ii
is
7
4
9
9
10
16
',3
8
4
14
2
1
"l
'6
i
11
0
2
2
2
3
3
18
0
0
0
0
6
12
1
2
4
7
6
11
3
18
26
6
26
26
15
30
26
0
24
23
28
28
26
25
8
30
30
30
30
io
'6
22
24
17
14
14
3
24
4
0
'2
0
0
33
0
0
0
3
22
~4
0
32
0
33
12
0
0
31
18
4
14
0
0
0
0
3
8
0
34
23
24
0
34
24
46
47
. 0
0
0
5
0
0
'6
0
9
0
0
o
B
0
0
0
0
0
3
0
2
0
1
0
0
0
0
0
1
0
0
2
0
3
2
'2
1
46
48
48
10
48
48
48
45
17
41
48
14
48
15
36
48
48
14
30
42
34
47
48
48
48
45
40
47
14
25
22
48
11
22
'6
0
Alternanthera E.A.C. ; . . .
' ' E.A.F
Amaranthus
Aster
Bean
Beet
Begonia
Carnation R.K
E.O
E.H
E.S
E.2
E.F
B.M.2
R.107
E.F.2
Carrot
Cauliflower
Chenopodium
Clover
Coleus I
" II
Corn
Cotton I ....
" II
" III
Dianthus barbatus S.M. .
N.P..
plumarius
sequeri
Eggplant I .
II
Lavatera
Lettuce
Poinsettia
Potato E.P.C.
E.P.I
" E.P.O .
" B.Sol
Salvia
Sedum
Sugar cane
Thistle
Check
} j
> >
"This strain had been in culture for a number of years; the exact year of
isolation is not known.
PARASITIC RUIZOCTONIAS IN AMERICA
343
FIG. 18. — EXPERIMENTS 1 AND IA: CARNATION CUTTINGS INFECTED WITH RHIZOC-
TONIA STRAINS (1) CARNATION R.K. ; (2) CARNATION R. 107; (3) CAR-
NATION R.O.; (4) CARNATION R.F. (5) BEGONIA; (6) COLEUS; (7) POIN-
SETTIA; (8) SALVIA; (9) CAULIFLOWER; (10) THISTLE; (11) LETTUCE;
(12) POTATO R.P.C.; (13) COTTON; (14) BEAN; (15) POTATO R.P.O.; (16)
CARROT
344 BULLETIN No. 189 [June,
The percentage of infection was about the same with all the carna-
tion strains except "Carnation R.O.," which appeared to have lost
practically all power of attacking cuttings. This was one of the first
strains isolated from carnation. Thus the age of the strain seemed
to play an important role in its virulence, and for this reason the date
of the original isolation of each strain is included in the table.
The strains from alternanthera, coleus, salvia, and poinsettia, all
cf which were isolated from diseased plants in the same cutting bench,
produced in some cases a soft wet rot of the carnation cuttings similar
to that caused by the carnation strains. In the majority of cases, how-
ever, these strains attacked the cuttings at the callus, forming large
browrn sclerotia which covered the whole callus and so prevented the
formation of roots. Brown strands of the mycelium and sclerotia
were formed on all parts of the cuttings underground and also be-
tween the leaves. Occasionally, small lesions appeared at the leaf
bases which were slightly under the surface of the sand.
The two strains from alternanthera and the one from poinsettia
killed about the same number of cuttings as the strains from carna-
tion, while the one from coleus caused 100-percent infection and rotted
the cuttings off faster than the strains from carnation. The percent-
age of infection with the strain from salvia was very low.
The strain from begonia produced a soft rot somewhat different
from that produced by the carnation strains. It appeared on the stem
at the surface of the soil and sometimes at the callus. The fungus
formed a dense mass of mycelium which completely covered the sand
beneath. Here again the virulence was greater than with the carna-
tion strains, all the cuttings being killed and in a much shorter time.
The strains from eggplant, lettuce, and thistle for the most part
formed many sclerotia on the stems and in between the leaves of the
cuttings, with only an occasional sclerotium at the callus. Small
lesions were found to be abundant at the leaf bases and on the stems.
These strains were very weak, especially those from lettuce and thistle,
which had been in culture for a number of years.
The cuttings infected with strains from cotton, cauliflower, and
sugar cane rotted off at the surface of the soil; the rot started as a
lesion at this point and progressed very rapidly until the cutting was
killed. Smaller lesions were produced on the stem underground.
Sclerotia and the brown strands of the fungus could be found in
abundance on the parts below the soil. The strains from cotton and
cauliflower were very virulent; all the cuttings inoculated with them
were killed one week before the cuttings inoculated with a soil culture
of the carnation strains began to die off.
The potato strains, as a rule, produced a large number of sclerotia
and a dark brown mycelium below the soil and on the leaves. The
percentage of infection was fairly high and uniform altho the average
was below that of the carnation strains.
1916] PARASITIC RHIZOCTONIAS IN AMERICA 345
The strains from alfalfa, bean, and carrot produced symptoms simi-
lar to those from potato. A large number of the cuttings placed in
the uninoculated sand wilted, but none became diseased.
During the spring of 1914, beginning on March 7 and ending on
April 7, the experiment was repeated, the only difference being that
a number of additional strains were used and flats containing forty-
eight cuttings instead of thirty. As will be seen in Table 3, the re-
sults were confirmatory. The marked increase in the virulence of the
lettuce strain may have been due in part to the influence of tempera-
ture both on the strain and on the cuttings.
EXPERIMENTS 2 AND 2A; INOCULATION OF YOUNG CARNATION PLANTS
WITH VARIOUS STRAINS OF RHIZOCTONIA
That the majority of strains can attack carnation cuttings was
shown in Experiments 1 and la, where it appeared that the virulence
of the strain did not depend on the host from which it was originally
isolated, but in some cases did depend on the length of time since the
culture was isolated. To determine whether rooted plants were as
susceptible to these various strains of Rhizoctonia as were cuttings,
further experiments were carried out : Experiment 2 in 1913, involv-
ing about 400 young plants and 24 strains; and Experiment 2a in
1914, in which about the same number of plants but only 13 strains
were used.
Carnation cuttings (White Enchantress) which had been placed in
sterilized sand December 12, 1912, were planted February 12, 1913,
in sterilized flats (9x12 inches) containing sterilized soil, fifteen plants
in each flat. Plants failing to strike root were pulled out, leaving an
unequal number in the various flats. The flats were inoculated on
March 23 with 250-cc. soil cultures of Rhizoctonia, each flat with a
different strain. They were then placed in a case in the greenhouse
and left during April and May.
Usually the carnation strains, as in the case of the cuttings (Ex-
periments 1 and la) , produced a soft, wet rot at the surface of the soil
or just below. On other plants they caused small lesions of various
sizes along the stems, killing the plants slowly. Sclerotia and brown
strands of mycelium were as a rule present on plants which showed
lesions and on others less badly diseased.
Only an occasional plant in the flats infected with other strains
than carnation developed a soft, wet rot. In the majority of cases
where infection took place the strains produced lesions of various sizes
on the stems at the surface of the soil or just below, slowly killing the
plants (Fig. 13). As a rule, sclerotia and mycelium were also present
on the stems of the infected plants. The plants in the check flat re-
mained healthy.
346
BULLETIN No. 189
[June,
The resistance of the rooted carnation plants to the fungus, as
shown in Table 4, was much more marked than with the cuttings. In
the few exceptions the fungus appeared able to infect the plants al-
most as readily as it had the cuttings.
In 1914 this experiment was essentially repeated. Thirty young car-
nation plants (Rosette) were placed in each of a number of flats
(12x18 inches) . On April 26, after the plants were rooted, some of the
old infected sand from the inoculated flats used in Experiment la was
mixed with the soil in which the plants were growing. The experiment
was continued until June 1. The results, which are presented in
Table 4, were similar to those of Experiment 2. As in that experiment,
the plants in the check flat remained healthy, with the exception of
two that wilted and died from attacks of a Fusarium.
TABLE 4. — SUSCEPTIBILITY OF YOUNG ROOTED CARNATION PLANTS TO VARIOUS
STRAINS OF RmzocTONrA: EXPERIMENTS 2 AND 2A
Strain
Number of plants
Experiment 2: 1913
Experiment 2a: 1914
Total {Healthy] Dead
Total
Healthy) Dead
Alternanthera R A.C
15 -
15
12
5
ii
2
'i
6
2
0
2
4
13
9
9
2
8
10
'G
13
15
7
8
10
13
12
15
3
10
'i
12
is
7
12
15
12
11
2
6
6
13
7
4
-9
'2
0
7
6
5
2
2
0
30
30
30
30
30
30
30
30
30
30
30
30
30
SO
is
25
20
is
is
io
22
23
13
12
24
19
24
28
12
5
10
15
15
20
's
7
17
18
6
11
'6
'JJ-
" R.A.F
Amaranthus
Beet
Begonia
15
14
Carnation R »K
R.H
R.S
14
13
14
15
14
15
15
15
15
15
15
14
15
15
15
14
14
15
15
14
15
R.2
R.F
R.F
R.M.2
R.107
R.F.2
Carrot
Cauliflower
Coleus I
Cotton I
" II
" III
Dianthus barbatus N.P
Efjtmlant I .
Lavatera
Lettuce
Potato R.P.C
" R.P.I
" R.P.O
Salvia
Sedum
Sugar cane
Thistle
Check
»
"Killed by Fusarium.
1916]
PARASITIC RHTZOCTONIAS IN AMERICA
347
EXPERIMENT 3: INOCULATION OF OLD CARNATION PLANTS IN POTS
WITH VARIOUS STRAINS OF RHIZOCTONIA
The resistance of young rooted carnation plants to the various
strains of Rhizoctonia other than those from carnation was very
marked in Experiments 2 and 2a. To determine whether or not old
carnation plants were even more resistant, the following experiment
was carried out, involving 90 plants and 18 strains.
Carnation plants (White Enchantress and White Perfection)
were brought in from the field and planted in pots, which were then
placed in the bench. The plants were grown under the best possible
cultural conditions and on November 27, 1912, when they had become
firmly established, they were inoculated. Five plants of the same size
were used for each test, one being left as a check. The other four were
inoculated by placing a bit of infected green-bean plug near the stem
about one-half inch below the surface of the ground. The stems of
two plants of each test were slightly wounded before the plugs were
placed by them. Observations were discontinued on March 27, four
months later. The results are presented in Table 5.
Only two plants inoculated by contact died during the course of
the experiment, and both were killed by carnation strains. However,
where the stem was slit, the various strains were in most cases able to
infect and kill the plant. The check plants remained healthy during
the experiment.
TABLE 5. — SUSCEPTIBILITY OP OLD CARNATION PLANTS (IN POTS) TO VARIOUS
STRAINS OP RHIZOCTONIA: EXPERIMENT 3
Strain
Plants inoculated by
Check plants
Contact
Slit
Healthy I Diseased
Healthy
Diseased
Healthy I Diseased
Alternanthera R.A.F
2
2
2
2
1
1
2
2
2
2
2
2
2
2
2
2
2
0
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
1
. 0
2
1
0
0
0
0
1
0
0
1
2
2
o
2
2
2
1
2
0
1
2
2
2
2
1
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Carnation R.K
R.O
R.H
R.S.
R.2
R.F
R.M.2
R.107
Carrot
Cotton II
Eggplant I
Lettuce
Poinsettia
Potato R. Sol
" R.P.O
" R.P.I
Thistle .
348
BULLETIN No. 189
[June,
EXPERIMENT 4: INOCULATION OF YOUNG CARNATION PLANTS WITH
ISOLATED AND WITH REISOLATED STRAINS OF RHIZOCTONIA
The object of Experiment 4 was to compare the virulence of various
strains of Rhizoctonia when they were inoculated on carnation plants
for the first time, and after they had been inoculated on carnation
and reisolated. Fifteen strains, taken at random, and about 300 plants
were used.
On December 12, 1912, a number of carnation cuttings were made
and placed in sterilized sand. They were allowed to remain in the
sand until well rooted. On March 22, when the plants were from
four to six inches high and breaking nicely, they were placed in three-
inch pots in sterilized soil. They were then inoculated by placing a
bit of bean pod infected with Rhizoctonia near the stem just below the
surface of the soil. Table 6 gives the results obtained.
With seven strains the virulence of the reisolated fungus was
slightly greater than that of the original isolation. With two it was
slightly less.
TABLE 6. — COMPARATIVE VIRULENCE OF ISOLATED AND EEISOLATED STRAINS OP
EHIZOCTONIA WHEN INOCULATED ON YOUNG CARNATION PLANTS (IN POTS) :
EXPERIMENT 4
Strain
Original isolation
Reisolation
Healthyl Diseased
Healthy! Diseased
Bean
9
6
1
4
*5
4
0
3
"(5
6
0
1
0
1
0
0
0
0
9
1
1
2
(5
7
4
3
7
5
10
7
10
8
9
1
9
9
8
5
3
6
7
3
5
0
3
0
2
1
Carnation B.K
R.K
E.H
5
G
10
7
R S
R2
R.F
R F
R.M.2
4
4
10
9
10
9
10
10
10
10
R.107
Cauliflower
Cotton I
" n
Potato RPI
Sugar cane
Check
> >
' ' •
EXPERIMENT 5: INOCULATION OF OLD CARNATION PLANTS IN THE
BENCH WITH VARIOUS STRAINS OF RHIZOCTONIA
Experiment 5 was similar to the preceding experiment except that
the carnation plants used were older and were grown in the bench in-
stead of in pots, and that inoculations were made with only eight
strains of Rhizoctonia, chosen at random.
1916} PARASITIC KHIZOCTONIAS IN AMERICA 349
On September 1, 1913, the soil in two five-foot sections in the green-
house was sterilized, and twenty carnation plants from the field were
placed in each section, four plants in a row. Four rows in each sec-
tion were each inoculated with a different strain of Ehizoctonia, by
means of pieces of infected bean plugs. The middle row in each sec-
tion was left as a check.
The plants began to die off at the end oi three weeks and con-
tinued dying until the close of the experiment, October 31. They all
died in a manner characteristic of stem rot. All the strains used
proved to be virulent except the one from beet (see Table 7). The
check plants remained healthy thruout the experiment.
TABLE 7. — SUSCEPTIBILITY OP OLD CARNATION PLANTS (IN THE BENCH) TO
VARIOUS STRAINS OF EHIZOCTONIA: EXPERIMENT 5
Strain ]Healthy | Diseased
Beet
3
1
Carnation R.107
0
4
Cauliflower
1
3
Cotton II
0
4
Dianthus barbatus S.M
1
3
plumarius .
0
4
Eggplant I .•
1
3
Potato B. Sol
1
3
Check
4
0
7 >
4
0
The high mortality of the strains in this experiment was due, to a
large extent, to the date of inoculation. The plants in the preceding
experiments were inoculated either late in the fall or in the early
spring, when the temperature in the greenhouse was low and normal
and not influenced by outside conditions. The temperature in the
house during September and October, when these plants were inocu-
lated, is very high ; hence the virulence of the fungus was much greater.
The effects of inoculating plants at various times of the year are
clearly brought out in the next experiment.
EXPERIMENT 6 : INOCULATION OF CARNATION PLANTS WITH Rmzoc-
TONIA AT DIFFERENT TEMPERATURES
During the season 1913-14 a number of sections containing carna-
tions were reserved in the greenhouse, and at different times of the
year the plants were inoculated with RMzoctonia from carnation.
This experiment was for the purpose of ascertaining the relative
virulence of Rhizoctonia when inoculated on carnation plants at dif-
ferent temperatures.
Each section contained twenty plants, sixteen of which were in-
oculated by placing infected bean plugs at the base of the stem. The
remaining four plants served as checks.
350
BULLETIN No. 189
[June,
TABLE 8. — RELATIVE VIRULENCE OF EHIZOCTONIA INOCULATED ON CARNATION
PLANTS AT DIFFERENT TEMPER \TURES: EXPERIMENT 6
Section
Date of
inoculation
Experiment
discontinued
Inoculated plants
Check plants
Healthy
Diseased
Healthy 1 Diseased
143
Sept. 1, 1913
Oct. 1, 1913
1
15
4
0
140
Oct. 1, 1913
Nov. 1, 1913
3
13
4
0
139
Nov. 1, 1913
Jan. 1, 1914
10
6
4
0
138
Dee. 1, 1913
Feb. 1, 1914
8
8
4
0
137
Jan. 1, 1914
Mar. 1, 1914
14
2
4
0
134
Feb. 1, 1914
Apr. 1, 1914
3
13"
4
0
133
Mar. 1, 1914
May 1, 1914
12
4
4
0
132
Apr. 1, 1914
June 1, 1914
9
7
4
0
131
May 1, 1914
July 1, 1914
0
16
4
0
130
June 1, 1914
July 1, 1914
2
14
4
0
128
July 1, 1914
July 23, 1914
6
10
4
0
•Ten plants found infected April 1; only three plants died during the months
of February and March.
As can be seen from Table 8, the death rate of the plants inocu-
lated on September 1 and October 1 was almost 100 percent. This
rate diminished very markedly when the plants were inoculated later
in the season, increasing with the plants inoculated during the spring
months until with those inoculated on May 1, it had again reached a
high percentage. This condition prevailed during the summer months,
showing very noticeably the influence of temperature on mortality.
EXPERIMENT 7: INOCULATION OF VARIOUS HOSTS (SEEDLINGS) OTHER
THAN CARNATION WITH VARIOUS STRAINS OF RHIZOCTONIA
In the preceding experiments all the work was carried on with
carnation plants of different ages. It was found that under certain
conditions all the strains used could attack these plants, but that the
resistance was somewhat increased when the plants were rooted. To
determine whether the same results could be obtained with other
plants, a number of further experiments were made.
Small flats (8x10 inches) were disinfected and filled with a mix-
ture of sterilized sand and soil suitable for germinating seed. In each
flat a 250-cc. soil culture of one of the various strains used was thoroly
mixed with the soil, and the whole allowed to stand for several days.
The seeds, after a short soaking in formalin (1-150), were sown in the
flats, thirty-one in all, care being taken not to plant them too closely.
Nine different kinds of seedlings and 13 strains wrere used in the ex-
periment. The results obtained are given in Table 9.
In the first group of the various hosts, clover proved to be more
resistant than alfalfa, while the injury to corn roots was negligible.
Of the different strains, the one from clover proved the most virulent,
while the one from corn was the weakest (Fig. 19).
1916]
PARASITIC EHIZOCTONIAS IN AMERICA
351
TABLE 9.-
-SUSCEPTIBILITT OF VARIOUS PLANTS (SEEDLINGS) OTHER THAN CARNA-
TION TO VARIOUS STRAINS OF KHIZOCTONIA: EXPERIMENT 7
Group 1
Strain
On clover
On alfalfa
On corn
Olov6r
150 seeds
150 seeds
30 seeds
Most of seedlings
killed at germina-
tion; 6 came up;
5 infected below
surface of ground,
showing lesions ;
1 healthy
All seeds attacked
by fungus at ger-
mination. Ehizoc-
tonia present in
seeds
Plants 4-6 inches
high. Seed in all
cases showed the
presence of Bhi-
zoctonia, but
whether it would
kill the whole
Alfalfa ....
Abbut 15 percent
80 percent damped
plant is a ques-
damped off in typ-
ical manner. Le-
sions at surface of
ground
off. Others in va-
rious stages of in-
fection. 5 percent
healthy
tion. However,
fungus is able to
live in the roots
of the corn. Cul-
Carnation R. 107. .
Only few plants
infected. First
leaves of a large
number dead from
effects of fungus
70 percent damped
off. Condition sim-
ilar to that of
plants inoculated
with alfalfa strain
tures of Ehizoc-
tonia were ob-
tained from the
seeds
Corn
2 percent damped
8 percent damped
off. Ehizoctonia
present on the
roots of living
plants, but did not
seem virulent
off. Eemaining
plants healthy
Group 2
Strain
On lettuce
On eggplant
On cabbage
Lettuce
150 seeds
150 seeds
90 percent damped
off. Lesions on
stem at surface
of ground. Leaves
also attacked,
causing a rot
2 percent damped
off. Lesions at
surface of ground.
Typical
Eggplant I
75 percent damped
3—4 percent damped
off. Lesions typi-
cal, like lettuce
off. Typical
Thistle
(50 percent damped
5 percent damped
off. Lesions typi-
cal, like those ori
plants inoculated
with eggplant
strain. Action of
fungus slower but
virulent
off. Small circular
lesions present.
Typical
Carnation E.F
60 percent damped
off. Like thistle ;
slower in effect,
but still virulent
All healthy
40 percent infected.
Lesions in form
of a collar
around stem at
surface of ground
Cauliflower
3 percent damped
Only 3 plants
off. Typical le-
sions
healthy. Seedlings
attacked at ger-
mination
352
BULLETIN No. 189
TABLE 9. — Concluded
[June,
Group 3
Strain
On radish
On turnip
On beet
Radish
150 seeds
150 seeds
1 percent infected
at base of stems.
Several completely
rotted
Seedlings attacked
at germination.
Only 2 healthy
plants
Potato R.P.C. . . .
15 percent infected
at base of stems
where root begins.
Small wounds like
potato scab due
to Rhizoctonia
off. Some rotted
off at the ground
Carrot
Seedlings attacked
50 percent infected
at germination.
Only 3 healthy
plants
All showed collar
rot. Some rotted
off
Carnation R.F. . .
50 percent infected.
Lesions at base of
stems. Few rotted
off
98 percent damped
off. Showed collar
rot. Typical
FIG. 19. — EXPERIMENT 7 : UPPER Row : ALFALFA SEEDLINGS INFECTED WITH
RHIZOCTONIA STRAINS (1) CLOVER; (2) ALFALFA; (3) CARNATION R. 107!
(4) CORN. LOWER Row: LETTUCE SEEDLINGS INFECTED WITH RHIZOCTONIA STRAINS
(1) LETTUCE; (2) EGGPLANT I; (3) THISTLE; (4) CARNATION R.F.
Of the seedlings in the second group, lettuce and cabbage were
quite susceptible ; eggplant seedlings were very resistant. The strain
from cauliflower, altho it caused only a slight damping-off of lettuce
1916] PARASITIC EHIZOCTONIAS IN AMERICA 353
seedlings, produced practically 100-percent infection in the case of
cabbage seedlings (Fig. 19).
In the third group, beet, radish, and turnip seedlings proved very
susceptible to damping-off of Rhizoctonia. It is rather interesting to
observe that while the strain from radish was able to cause only
1-percent infection of radish seedlings, it caused almost 100-percent
infection of turnip seedlings.
Taking the experiment as a whole, it is seen that a great variation
exists in susceptibility of seedlings and in virulence of strains. It is
clear that under certain conditions all the strains can attack a given
host with about the same virulence.
EXPERIMENT 8: INOCULATION OF VARIOUS HOSTS (OLD) OTHER THAN
CARNATION WITH VARIOUS STRAINS OF RHIZOCTONIA
In Experiment 8 the preceding experiment was carried one step
farther, older plants being used rather than seedlings. A number of
plants were taken from flats while small and transplanted to four-inch
pots, where they were allowed to grow for about two months. The
soil in these pots was not sterilized. Each plant, with the exception of
the check plants, was inoculated by placing an infected bean plug in
contact with it just below the surface of the soil. Four kinds of
plants, 50 of each, and 12 strains were employed. The observations
from this experiment are recorded in Table 10.
In Group 1, the tomato plants proved resistant to the attacks of
the various strains, with the exception of the one from carnation, which
produced a slight infection on two plants. In the case of the cabbage
plants, the strains from cotton and from cauliflower exhibited a marked
specialization, producing 50- and 90-percent infection, respectively, on
these plants, while on tomato plants they produced no infection what-
ever. Cabbage was the only host in the experiment susceptible to all
the strains with which it was inoculated.
The carnation strains in Groups 2 and 3 also proved more virulent
than the other strains, producing 50-percent infection on lettuce and
100-percent infection on beet (Fig. 9). Of the other strains, eggplant
alone was able to attack the plants, producing a slight infection on
two lettuce plants.
EXPERIMENT 9: INOCULATION OF VARIOUS HOSTS (CUTTINGS, SEED-
LINGS, AND LARGER PLANTS) WITH VARIOUS STRAINS OF RHIZOCTONIA
The kinds of plants used in the foregoing experiments were some-
what limited. Increased facilities being at hand in the spring of 1914,
a more extensive series of inoculations was made with cuttings, seed-
lings, and larger plants of various kinds. In all, about 350 cuttings,
3.000 seedlings, and 300 larger plants were inoculated. Thirty-two
strains of Rhizoctonia were used.
354
BULLETIN No. 181)
[June,
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1916] PARASITIC RHI/.OCTONIAS IN AMERICA 355
Flats (9x12 inches) were infected as in Experiment 7, and a vary-
ing number of cuttings, seeds, and plants placed in them on March 7,
1914. Pure cultures from the diseased plants in each flat were made,
and Rhizoctonia was isolated in each case. Following, the results of
the experiment are taken up in detail.
" Alternanthera E.A.C." on Alternanthera. — 48 cuttings. On March 18 all
were dead. The infection was first noticed as a small, brown lesion on one side
at the surface of the ground; later the lesion girdled the whole stem. The fun-
gus also attacked the cut surface of the cutting, causing a lesion and in some
instances a slow, wet rot. The mycelium, which grew very profusely, attacked
the leaves, producing a characteristic rot.
"Alternanthera E.A.F." on Alternanthera. — 48 cuttings. The experiment
was carried out exactly like the above and produced the same results.
"Alternanthera E.A.F." on Gernanium. — 48 cuttings. These were planted
March 20 in the infected flat in which alternanthera cuttings had died. By
May 2, 42 of them were rotted while 6 were rooted and healthy.
"Amaranthus" on Amaranthus salicifolius. — 100 seeds. Seeds germinated
March 23, and by April 1 all the plants in the flat damped off in a character-
istic manner.
"Aster" on Aster. — 100 seeds. Seeds germinated March 18 and a few be-
gan immediately to damp off. By April 1, 29 percent had died, while the others
remained healthy.
"Bean" on Bean. — 30 seeds. Seeds germinated March 19, and after two
months only 5 percent were killed by the fungus. .
"Beet" on Beet. — 100 seeds. Seeds germinated March 19 and began to
damp off. About 25 percent damped off and later about 25 percent more be-
came scabby because of the formation of small, depressed lesions. Injury here
was similar to the infection of beet by the strains from carnation.
' ' Carnation ' ' on Bean. — 50 plants. On May 8, bean plants about three
inches high were transplanted from flats to infected sections (Nos. 157 and
173). The plants took hold readily, and after about two weeks began to show
signs of infection. The disease progressed rather slowly ; most of the plants
produced a few pods before they were killed by the fungus. When pulled up,
May 19, every one was diseased or dead (Fig. 8). A detailed description of
four typically infected bean plants follows. It will be seen that it corresponds
in most details to the descriptions given by Barrus,9 Fulton,45 and Hedgcock60
Plant No. 1: Three distinct lesions were present, one directly
above the other on the stem. Lesions were oval in shape with a reddish
brown band surrounding a lighter colored sunken area. Evidences were
present of young lesions over the entire stem and larger roots under-
ground. The wounds extended beneath the cortical layer to the woody
tissue.
Plant No. 2: Eoots were infected at the joint of their union with
the main stem. The lateral root was very badly infected and rotted off
entirely. The lesions on the smaller roots were small, depressed, and of
a reddish brown color.
Plant No. 3: A large, reddish brown lesion extended from the sur-
face of ground downward 2.5 centimeters. Spots were sunken and ex-
tended thru the cortex to woody tissue beneath. Two small sunken areas
of a reddish brown color were present on the stem one inch above the sur-
face of the ground.
Plant No. 4 : A large, depressed, reddish brown area extended from
the surface of the ground downward 2.5 to 3 centimeters, almost encircling
the stem. Cortical tissue rotted away exposing the woody tissue beneath.
"Carnation" on Beet. — 30 plants. On May 8, young beet plants were trans-
planted to a section (No. 158) infected with Rhizoctonia from carnation. By
356 BULLETIN No. 189 [June,
May 20 they all showed some scab. A number were infected at the crown, where
a large number of leaves were completely cut off at the base by the fungus. Sev-
eral beets had depressed lesions which extended deep into the tissues.
"Carnation" on Cabbage. — 25 plants. On May 8, young cabbage plants
were transferred from flats to a section (No. 163) in the greenhouse infected
with a soil culture of Khizoctonia from carnation. Some of these plants grew
to maturity, but when they were pulled up, May 21, the stems and roots were cov-
ered with black, depressed lesions (Fig. 11). Ninety percent of the plants set in
the bench were infected in this way. Where the leaves touched the soil the fun-
gus caused a slow, wet rot.
' ' Carnation ' ' on Carrot. — 50 plants. Carrot plants were transferred on
May 8 from flats to an infected section (No. 158) in the greenhouse. By May
21 only a few had rotted. The rot started at the crown, where the petioles were
attacked, and worked down into the tissues of the root and up into the leaves.
The rot from the crown goes into the interior of the root, and thus the root does
not show any signs of rot on the outside for some time. Occasionally lesions
were found on the sides of the carrots and on the larger roots where they branched
from the fleshy part.
"Carnation" on Corn. — 10 seedlings. Corn seedlings about 8 inches tall
were transplanted on May 8 from flats to an infected section (No. 153) in the
greenhouse. The plants grew to maturity. When pulled up, only small lesions
were to be found on the roots. These were only slightly depressed and did not
retard the growth of the plant.
"Carnation" on Eggplant. — 25 plants. On May 8, eggplants were trans-
ferred to an infected section in the greenhouse (No. 170). The plants reached
maturity with no loss. When they were pulled up, no infection was to be found.
"Carnation" on Lettuce. — 60 plants. On March 16, lettuce plants were
transferred to an infected section (No. 153). By March 24, 16 percent of the
plants were killed. No more loss occurred and the plants were cut on April 21.
"Carnation B. 107" on Cabbage. — 100 seeds. Seeds germinated March 19
and began to damp off immediately. By May 21 those which did not damp off
were infected in various ways. Some had constrictions just at the surface of the
soil; others had definite lesions along the stern and larger roots. Where the plants
were crowded, spots of various sizes were formed on the lower leaves which touched
the soil.
' ' Carnation E.M.2 ' ' on Carrot. — 150 seeds. Seeds germinated March 18.
When the experiment was discontinued, May 21, only 10 percent of the carrots
were infected at the crown. One showed a constriction which was quite marked.
"Carnation R.F." on Beet. — 100 seeds. Seeds germinated March 16 and
began to damp off immediately, so that by March 24, 40 percent of the plants
were dead. The remainder, when examined on May 21, were all more or less
scabby. Some were rotted at the crown.
' ' Carnation E.F.2 ' ' on Bean. — 30 seeds. Seeds germinated March 19. When
the experiment was discontinued, May 8, but slight infection could be noticed.
"Carrot" on Carrot. — 150 seeds. Seeds germinated March 16. By May 21
only a few of the carrots were infected. An occasional plant showed crown rot,
which was especially noticeable at the base of the leaves.
"Cauliflower" on Cabbage. — 100 seeds. Seeds germinated March 13. A few
seedlings began to damp off March 14 and by May 21 most of the plants were
infected. Lesions could be found on the stems, occasionally one girdling the whole
stem and forming a sort of constriction as the plant developed. A number of
spots varying in size could also be found on the lower leaves which touched the
soil.
"Chenopodium" on Alfalfa. — 100 seeds. Seeds germinated March 13. Two
weeks later 60 percent of the seedlings had damped off in a characteristic manner.
"Clover" on Clover. — 150 seeds. Seeds germinated March 12 and began
to damp off slowly. By March 21, however, the plants had reached sufficient
size so that no more damping-off occurred. In all about 10 percent of the seed-
lings were diseased.
1916] PARASITIC BHIZOCTONIAS IN AMERICA 357
"Coleus I" on Coleus. — 100 seeds. The seeds were all killed by the fun-
gus as they were germinating.
"Coleus I" on Coleus. — 48 cuttings. By March 18 all the cuttings had
rotted off. Infection began as small spots at the surface of the ground or at
the callus. Underground lesions of all sizes were produced, from small spots to
places where the whole stem was girdled. The leaves of the cuttings were over-
run with mycelium, the fungus in many cases rotting them off.
"Coleus II" on Chrysanthemum. — 48 cuttings. The old infected flat in which
the coleus cuttings had rotted off was planted to chrysanthemum cuttings March
20. By March 27 all of them had rotted off at the surface of the ground. In
some a soft, wet rot was produced.
"Coleus II" on Coleus. — 100 seeds. Seeds germinated March 24 and began
to damp off slowly. By May 21 only 30 percent of the plants were still healthy.
"Coleus II" on Coleus. — 48 cuttings. All cuttings rotted off as with "Coleus
I. ' ' The red-colored cuttings rotted off faster and were much more susceptible
than those of the green variety.
"Corn" on Corn. — 50 seeds. Seeds germinated March 17. The plants grew
to maturity. When pulled up, no signs of infection were noticed.
"Cotton I" on Cotton. — 50 seeds. The fungus caused a rotting of the seeds
as they germinated.
"Cotton III" on Cotton. — 50 seeds. Eesults same as preceding.
"Dianthus barbatus S.M." on Dianthus barbatus (Sweet William). — 100
seeds. Seeds germinated March 19 and began to damp off immediately. By May
22, 50 percent of the seedlings were diseased.
"Dianthus barbatus N. P." on Dianthus barbatus (Sweet William). — 100
seeds. Eesults same as preceding.
' ' Dianthus plumarius ' ' on Dianthus plumarius. — 100 seeds. Seeds germinated
March 14. By May 22, 80 percent of the plants had damped off.
"Dianthus sequeri" on Dianthus sequeri. — 100 seeds. Seeds germinated
March 18 and began to damp off immediately. By May 22 only about 25 percent
were still healthy.
"Eggplant I" on Eggplant. — 150 seeds. Seeds germinated March 23. By
May 8 only 3 to 4 percent of the plants had damped off.
"Eggplant II" on Eggplant. — 150 seeds. Seeds germinated March 23. The
fungus caused a rot of the seeds at germination.
"Lavatera" on Lavatera trimestris. — 100 seeds. Seeds germinated March
12. By May 22 about 25 percent of the seedlings had damped off (Fig. 14)..
On the remainder, lesions of various sizes were present, which in some cases girdled
the stem just below the surface of the soil and formed a collar, or constriction.
' ' Lettuce ' ' on Lettuce. — 125 seeds. Seeds germinated March 13. By April
1 all the young plants had damped off.
"Poinsettia" on Euphorbia variegata. — 100 seeds. Seeds germinated March
23. By May 22, 6 percent of the plants had damped off.
"Salvia" on Salvia splendens.- — 100 seeds. Seeds germinated March 23. By
May 8, 6 percent of the seedlings had damped off. By May 21, 4 of the plants
were infected. Lesions extending into the woody tissues were present on the stem.
"Salvia" on Salvia splendens. — 48 cuttings. These cuttings rotted off very
rapidly. Wherever the leaves touched the soil, they were rotted also. By April
7, 41 cuttings were diseased and 7 were rooted and healthy.
"Sugar Cane" on Amaranthus salicifolius. — 100 seeds. Seeds germinated
March 23. On May 21 all the plants were perfectly healthy. No infection waa
present.
"Thistle" on Clover. — 100 seeds. Seeds germinated March 13. On May 21
all the plants were healthy.
Additional Inoculations. — On April 1 six flats of infected soil used in the
inoculation experiments with carnation cuttings were mixed with soil in larger
tlats and four hills of potatoes were planted in each. The six flats represented the
358 BULLETIN No. 189 [June,
six strains " Alternanthera B.A.F.," "Carnation R.F.," "Cauliflower," "Let-
tuce, ' ' " Cotton, ' ' and ' ' Dianthus barbatus. ' ' Only one or two potato sprouts
came up from each hill and these were weak and spindling. After the tempera-
ture became too high in the greenhouse, the flats were placed outside, so that the
plants would develop further and produce tubers. The strains killed some of the
young sprouts and dwarfed the others, showing that they were able to attack the
potato plant.
Here, as in the preceding experiments, the death rate of the vari-
ous plants was quite variable. These differences appear to be due to
the virulence of the fungus, to the susceptibility of the plant, or to a
combination of factors.
EXPERIMENT 10 : INOCULATION OF VARIOUS HOSTS IN THE FIELD
WITH VARIOUS STRAINS OF RHIZOCTONIA
All the inoculation experiments reported so far were conducted in
the greenhouse. In the summer of 1914 a fourth of an acre of land was
divided into three parts, separated by six-foot strips of ground. Sec-
tion 1 was inoculated on May 20 with twenty cubic feet of infected soil
taken from the inoculated benches in the greenhouse. The soil was
spread upon the section, worked under, and watered for several days.
Section 2 was left as a check. In Section 3 small bits of pure cultures
of various strains of Rhizoctonia were added with the seeds and plants.
The seeds were planted May 20, and the young plants were put in
June 16. Altho the drouth of the summer interfered considerably,
the results obtained were sufficient to show that Rhizoctonia Solani
was active under field conditions as well as in the greenhouse.
No infection occurred in the first two sections. In Section 3 in-
fection was quite marked in a number of cases, especially on cotton,
potato, and several greenhouse plants. Where the strain ' ' Cotton I ' '
was added to the cotton seeds, 100-percent infection occurred. In the
case of potato, to which ' ' Carnation R.F.2 ' ' was added, a marked dif-
ference was noticed, the plants in this section being dwarfed and
spindling, while in the first two sections they were bushy and strong.
The difference in the yield was as marked as the difference in growth
of the plants. All the coleus plants infected with "Coleus I" were
killed within two weeks after being set out. The same results were
obtained from inoculating salvia plants with the strain from salvia.
DISCUSSION OF INOCULATION EXPERIMENTS
In Table 11 are brought together, in tabular form, the results of
all the inoculation experiments, with the exception of No. 4, which
was carried on primarily to test the comparative virulence of isolated
and reisolated strains of Rhizoctonia. The thing that stands out at
first glance is the great variation in the mortality of the plants when
inoculated with strains from the same host and when inoculated with
strains from other sources.
1016] PARASITIC KHIZOCTONIAS IN AMERICA 359
When carnation cuttings were infected, the strains used, with but
two exceptions, whether from carnation or from other hosts, were
able to cause more or less loss, the mortality of the cuttings ranging
in either instance from 0 to 100 percent. Again, the same strains
varied in virulence from one year to another, in most cases decreas-
ing in virulence with age. When cuttings other than carnation were
used, the results were the same.
When young rooted carnation plants were inoculated, the percent-
age of loss was much less than with cuttings. Here, however, the car-
nation strains seemed to be slightly more virulent than those from
other sources, altho there was still a great difference in the strains
from carnation themselves. Only one of the strains from other sources
was unable to attack young rooted carnation plants.
On old carnation plants in the greenhouse which were inoculated
by contact, even the carnation strains did not cause a high percentage
of infection. However, when plants growing under these same condi-
tions were slightly wounded and then inoculated, the percentage of
loss was very high in nearly all the strains studied. When conditions
(temperature and moisture) were favorable to the fungus, most of the
strains studied were able to infect carnation plants as readily as the
carnation strains themselves.
In the majority of cases all strains were able to cause damping-off
of various seedlings. There was a great difference in the virulence of
strains when inoculated on the same host from which they had been
isolated and when inoculated on other hosts. Only occasionally was
there any indication of marked specialization, and in no case was such
indication corroborated in succeeding experiments.
In older plants, a marked difference in susceptibility was found in
the different species. As a rule, the root crops were highly susceptible
to attacks of Rhizoctonia. Among these, beet appeared to be the most
susceptible. Tomato and eggplant showed a very marked resistance
to Rhizoctonia, and this was true to some extent of the potato also,
altho under certain conditions it was quite susceptible. This varia-
bility of resistance held true for most of the vegetable and field crops
other than root crops. Under ordinary conditions, the majority of
floricultural plants were not subject to attacks of Rhizoctonia, altho
the mycelium of this fungus was known to be present in the soil or
even on the plant itself.
From the fact that all the strains studied showed the ability to
attack the same species of plant and produce the same characteristic
symptoms, it seems clear that they can be included under one form,
A'. Solani. These experiments show further that the virulence of
R. Solani is very variable, as is also the degree of resistance of the vari-
ous host plants, both depending on a number of varying factors.
360
BULLETIN No. 189
[June,
TABLE 11. — SUMMARY OF INOCULATION EXPERIMENTS
Strain
Original
date of
isolation
Date of
inoculation
experiment
Host
Condition
Per-
centage
of loss*
Alfalfa
1910
1913
Alfalfa
Seedlings
95
Alternanthera R.A.C.
Alteruanthera R.A.F.
Amaranthus
1912
1912
1913
1913
1913
1913
1913
1913
1914
1913
1914
1913
1914
1913
1914
1913
1914
1913
1913
1914
1914
Cabbage
Carnation
Clover
Corn
Tomato
Alternanthera
Carnation
t >
)>
Alternanthera
Carnation
> >
i >
»
) t
»
Geranium
A maranthus
Plants
Cuttings
Seedlings
> t
Plants
Cuttings
> >
»
Young plants
Cuttings
a
»
Young plants
» »
Old plants
> > > >
(wounded)
Cuttings
20
38
15
0
0
100
92
96
20
100
90
100
66
40
0
50
87
Aster
1913
1914
1914
1914
salicifolius
Carnation
7 )
Aster
Seedlings
Cuttings
Young plants
Seedlings
100
100
16
29
Bean
1914
1914
Carnation
Bean
Cuttings
Seedlings
23
5
Beet
1913
1913
1914
1914
Carnation
t >
Beet
Cuttings
j >
Seedlings
65
100
^0
Begonia
1911
1914
1914
1913
1913
Carnation
Cuttings
Young plants
Old plants
Cuttings
100
33
25
ion
Carnation E.K
1911
1913
1913
Young plants
Cuttings
6
90
Carnation R.O
1911
1913
1913
1913
1913
Young plants
Old plants
» »
(wounded)
Cuttings
85
0
100
o
Carnation K.H.
1911
1913
1913
1913
Old plants
> i »
(wounded)
Cuttings
0
100
80
Carnation R.S
1911
1914
1914
1913
1913
1913
> )
Young plants
Old plants
» »
(wounded)
Cuttings
100
50
0
100
82
1913
1913
1913
Young plants
Old
» »
(wounded)
93
50
100
•In Experiments 1 and la the loss from plants wilted is not included in the
percentage of loss.
1'JIG]
PARASITIC RHIZOCTONIAS IN AMERICA
361
TABLE 11. — Continued
Strain
Original
date of
isolation
Date of
inoculation
experiment
Host
Condition
Per-
centage
of loss"
Carnation R.2
1912
1913
UaTnation
buttings
100
1913
) }
Young planb
54
1913
> >
Old plants
50
1913
i i
11 11
(wounded)
100
Carnation R.F
1912
1913
Beet
Seedlings
98
1914
) >
i >
40
1913
Cabbage
»
40
1913
Carnation
Cuttings
100
1914
j >
94
1913
Young plants
85
1913
j j j >
100
1914
1 1 11
50
1913
Old plants
0
1913
11 11
(wounded)
100
1913
Eggplant
Seedlings
0
1913
Lettuce
1 1
60
1913
,• >
Plants
50
1913
Radish
Seedlings
50
Carnation R.M.2
'1912
1913
Carnation
Cuttings
96
1914
; i
) i
43
1913
1 i
Young plants
85
1913
' '
Old plants
0
1913
1 i
11 11
(wounded)
50
1914
Carrot
Seedlings
10
Carnation E 107
1912
1913
Alfalfa
11
70
1913
Beet
Plants
100
1914
Cabbage
Seedlings
75
1913
Carnation
Cuttings
92
1914
i i
11
91
1913
11
Young plants
73
1913
i i
Old plants
0
1913
i i
11 11
(wounded)
100
1913
> >
Old plants
100
1913
Clover
Seedlings
5
1913
Corn
11
0
Carnation R.F.2
1913
1914
Bean
11
3
1914
Carnation
Cuttings
100
1914
. i i
Yroung plants-
66
Carnation R.121-5. . .
1912
1913
Cabbage
Plants
70
1913
Tomato
11
20
Carnation (Sections
157 and
173)
1914
Bean
11
98
Carnation (Section
158)
1914
Beet
1 1
95
( 163)
1914
Cabbage
1 1
90
'( 158)
1914
Carrot
11
10
( 153)
1914
Corn
Seedlings
0
( 170)
1914
Eggplant
Plants
0
( 153)
1914
Lettuce
1 1
16
"See footnote, page 360.
362
BULLETIN No. 189
f June,
TABLE 11. — Continued
Strain
Original
date of
isolation
Date of
inoculation
experiment
Host.
Condition
Per-
centage
of loss"
1913
Beet
Plants
0
Cauliflower
1912
1913
1914
1913
1913
1913
1914
1913
1913
1913
Carnation
> j
> >
> t
> j
Carrot
Radish
Turnip
Cabbage
Cuttings
i }
Young plants
Old plants
» »
(wounded)
Seedlings
»
)>
66
30
13
0
0
5
98
50
98
Chenopodiuni
1913
1914
1913
1913
1914
1913
1914
1913
1913
1913
1914
,, &
> t
Carnation
»
»
»
> t
Lettuce
Tomato
Alfalfa
»
Plants
Cuttings
»
Young plants
» j >
Old plants
Seedlings
Plants
Seedlings
97
90
100
100
40
26
75
3
0
60
1912
1914
1913
Carnation
Alfalfa
Cuttings
Seedlings
31
100
Coleus I
1912
1914
1913
1914
1913
1913
Carnation
Clover
> j
Corn
Carnation
Cuttings
Seedlings
»
»
Cuttings
75
99
10
0
100
Coleus II
1913
1914
1913
1914
1914
1914
1914
j j
> j
»
Coleus
> >
Carnation
»
Young plants
» »
Seedlings
Cuttings
i j
100
40
23
100
100
100
Corn
1912
1914
1914
1914
1913
Chrysanthemum
Coleus
) >
Alfalfa
) >
Seedlings
Cuttings
Seedlings
100
70
100
g
Cotton I
1911
1914
1913
1913
1914
1913
Carnation
Clover
Corn
> >
Cabbage
Cuttings
Seedlings
> >
>t
Plants
51
2
0
0
50
Cotton II
1912
1913
1914
1913
1914
1914
1913
1913
Carnation
y >
) >
) >
Cotton
Tomato
Carnation
Cuttings
> >
Young plants
» > )
Seedlings
Plants
Cuttings
100
62
87
56
100
0
100
Cotton III .
1912
1914
1913
1913
1913
1913
1914
> >
Young plants
Old plants
» t>
(wounded)
Old plants
Cuttings
91
46
0
50
100
70
"See footnote, page 360.
1916]
PARASITIC KIIIZOCTONIAS IN AMERICA
363
TABLE 11. — Continued
Strain
Original
date of
isolation
Date of
inoculation
experiment
Host
Condition
Per-
centage
of loss*
Cotton III
1912
1913
Carnation
Young plants
28
1914
Cotton
Seedlings
100
Dianthus barbatus
g M
1913
1914
Carnation
Cuttings
98
1913
> }
Old pjants
75
1914
Dianthus
barbatus
Seedlings
50
Uiaiithusbarbatus N.P.
1913
1914
Carnation
Cuttings
100
1914
»
Young plants
60
1914
Dianthus
barbatus
Seedlings
50
Diauthus plumarius. .
1913
1914
Carnation
Cuttings
100
1913
> >
Old plants
100
1914
Dianthus
plumarius
Seedlings
80
Dianthus sequeri
1913
1914
Carnation
Cuttings
100
1914
Dianthus
sequeri
Seedlings
75
Kppnlant I
1912
1913
Carnation
Cuttings
42"
1914
> i
93
1913
Young plants
60
1914
) ) »
20
1913
Old plants
0
1913
> > > >
(wounded)
100
1913
»
Old plants
75
1913
Eggplant
Seedlings
3
1914
) i
> >
4
1913
Lettuce
> >
75
1913
»
Plants
20
Eggplant II
1913
1914
Carnation
Cuttings
83
1914
Eggplant
Seedlings
100
Lavatera
1913
1914
Carnation
Cuttings
98
1914
) )
Young plants-
36
1914
Lavatera
trimestris
Seedlings
95
Lettuce
1913
Carnation
Cuttings
0
1914
j >
i }
34
1913
i y
Young plants
13
1913
> >
Old plants
0
1913
) >
» > >
(wounded)
100
1913
Eggplant
Seedlings
2
1913
Lettuce
»
90
1914
»
100
1913
Plants
0
Poinsettia
1912
1913
Carnation
Cuttings
75
1914
> >
52
1913
Old plants
0
1913
» > •>
(wounded)
100
1914
Euphorbia
variegata
Seedlings
6
Potato E.P.C
1912
1913
Beet
»
50
1913
> >
Plants
0
1913
Carnation
Cuttings
90
1913
ft
Young plants
0
"See footnote, page 360.
364
BULLETIN Xo. 189
TABLE 11. — Concluded
Strain
Original
date of
isolation
Date of
inoculation
experiment
Host
Condition
Per-
centage
of loss*
Potato R.P.C
1912
1912
1912
1913
1912
1913
1913
1913
1913
1913
1913
1913
1913
1913
1913
1913
1913
1913
1913
1913
1913
1913
1914
1913
1914
1914
1914
1914
1914
1913
1914
1913
1913
1914
1913
1913
1913
1914
1913
1913
1914
Radish
Carnation
j>
> ;
j >
5 5
55
; >
> >
5 ;
5 >
; 5
Beet
Radish
Turnip
Carnation
5 5
»
Salvia
splendens
> >
Carnation
i 5
Amaranthus
salicifolius
Carnation
5
5
5
!
>
5 '
Clover
Eggplant
Lettuce
»
Seedlings
Cuttings
Young plants
Old plants
> 5 55
(wounded)
Cuttings
Young plants
Old plants
55 55
(wounded)
Cuttings
Old plants
55 55
(wounded)
Old plants
Plants
Seedlings
> }
Cuttings
. »
Young plants
Seedlings
Cuttings
7 )
Young plants
Seedlings
Cuttings
5 5
Young plants
Cuttings
55
Young plants
Old plants
55 ) 5
(wounded"
Seedlings
} 5
»
Plants
.15
65
50
0
100
58
43
0
50
60
0
100
75
0
1
99
2
47
33
10
85
100
20
0
90
24
13
33
47
1
100
0
5
60
0
Potato R.P.I
Potato R.P.O
Potato R Sol
Radish
Salvia
Sedum
Sugar cane
Thistle
"See footnote, page 360.
GROAVTII ON MEDIA
In the course of these studies thirty-eight strains of Rhizoctonia
were grown on five of the more common vegetable-extract agars and a
solid synthetic medium. The composition of these media may be found
in the appendix, together with a complete description of the growth
of the various strains on them.
1916] PARASITIC RHIZOCTONIAS IN AMERICA 365
As a rule the fungus isolated from carnation plants, when grown
on green-bean agar, produced a rapid-growing mycelium, which was
practically all aerial, loose, and tufted. The most characteristic fea-
ture was the production of concentric zones, tho this was not invaria-
ble. Of the many hundred cultures made during the past three years
from diseased carnation plants on green-bean agar, 90 percent have
shown this zonation. This characteristic was influenced by neither
light nor temperature. A typical growth on this medium is shown in
Fig. 20, "Carnation R.H." A few of the carnation strains grown
on the same medium and showing the same type of mycelium produced
very indistinct zonation or none, as shown in Fig. 20, "Carnation
R.F." Zonation persisted to some extent when the carnation strains
were grown on other media than green-bean agar, but it was not so
characteristic.
The two strains from potato did not grow so rapidly nor quite
so luxuriantly on green-bean agar as did the carnation strains, but
they produced the same even, tufted, zonate growth. Here the zones
were closer together. (See Fig. 20, "Potato R. Sol.")
The growth of the strain from corn on green-bean agar was similar
to that of "Potato R. Sol."
The growth on green-bean agar of the strains from eggplant, let-
tuce, Chenopodium, and thistle was different from any of the other
forms in that the mycelium grew along the surface, running out ra-
dially in strands, which became larger and more tufted at the edge.
(See Fig. 21, "Eggplant I.")
The strains isolated from alternanthera, coleus, salvia, and poin-
settia, when grown on green-bean agar, showed the same even, fluffy
to tufted growth. This was also characteristic of the strains from
cauliflower, cotton, and sugar cane. Zonation in these strains was
varied. (See Fig. 21.)
The strain from onion when grown on this agar differed radi-
cally from the others. The mycelium was bright colored, finer, and
almost all submerged. (See Fig. 20.)
The other strains studied on green-bean agar cannot be put in
definite groups, as they shade into one another. However, the growth
of the mycelium was somewhat similar in each case; practically the
only difference noted was in the extent of the zonation.
On corn-meal agar the growth of the strains was similar to a large
extent ; the only great difference noted was in rapidity of growth.
Zonation was very rare on this medium.
The growth of the strains on oat agar was somewhat variable;
zonation was sometimes present and sometimes absent.
The most characteristic feature of the growth of the majority of
the strains on potato agar was the turning brown of both the myce-
lium and the medium. This same characteristic, but to a less degree,
366
BULLETIN No. 189
[June,
FIG. 20. — CULTURES OF RHIZOCTONIA STRAINS SHOWING DEVELOPMENT OF MYCE-
LIUM ON GREEN-BEAN AGAR (CULTURE 48 HOURS OLD). Top Row: (1) CAR-
NATION R.H.; (2) CARNATION R.F. MIDDLE Row: (1) POTATO R. HOL.; (2)
CARROT. BOTTOM Row: (1) CAULIFLOWER; (2) ONION
1016]
PARASITIC RHizoctONlAS IN AMERICA
367
FIG. 21.— CULTURES OF BHIZOCTONIA STRAINS SHOWING DEVELOPMENT OF MYCE-
LIUM ON GREEN -BE AN AGAR (CULTURE 48 HOURS OLD). TOP Bow: (1) ALTER -
NANTHERA'B.A.F.; (2) ALTERNANTHERA B.A.C. MIDDLE Bow: (1) POIN-
SETTIA; (2) COLEUS I. BOTTOM Bow: (].)- EGGPLANT I; (2) LETTUCE
368
BULLETIN No. 189
f June,
FIG. 22. — CULTURES OF EHIZOCTONIA STRAINS SHOWING DEVELOPMENT OF SCLERO-
TIA: (1) ALTERNANTHERA R.A.C.; (2) SALVIA; (3) POINSETTIA; (4) ALTER-
NANTHERA E.A.F. ; (5) COLEUS ; (6) EGGPLANT II; (7) EGGPLANT I; (8)
LETTUCE; (9) CHENOPODIUM; (10) THISTLE; (11) CARNATION E.F.2; (12)
CARNATION E.S.; (13) CARNATION E.2; (14) CARNATION E.H.; (15) CARNA-
TION E.G.; (16) ASTER; (17) COTTON I; (18) BEET; (19). CARROT; (20)
BEAN
1916]
PARASITIC RHIZOCTONIAS IN AMERICA
369
FIG. 23. — CULTURES OF RHIZOCTONIA STRAINS SHOWING DEVELOPMENT OF SCLEHO-
TIA: (1) AMARANTHUS; (2) PANSY; (3) LAVATERA; (4) SWEET ALYSSUM;
(5) LOBELIA; (6) ALFALFA; (7) CLOVER; (8) CORN; (9) CAULIFLOWER; (10)
SUGAR CANE; (11) BUCKWHEAT; (12) RED CLOVER; (13) SEDUM; (14)
GYPSOPHILA; (15) ONION; (16) DIANTHUS BARBATUS S.M. : (17) DIANTHUS
PLUMARIUS; (18) DIANTHUS SEQUERI; (19) DIANTHUS BARBATUS N.P.; (20)
ASTER (CARNATION STRAIN)
370 BULLETIN No. 189 [June,
was found with the growth on potato-glucose agar. On both these
media zonation was usually lacking or indistinct.
On Agar XII most of the strains grew rather poorly and produced
a white, flaky growth, with varying zonation.
Early in the study of the characters of the strains on culture
media, it was noticed that as there were characteristic differences in
growth, so also were there differences in the production of sclerotia.
The strains "Eggplant I," "Lettuce," " Chenopodium, " and
"Thistle" on green-bean agar all formed sclerotia in a characteristic
manner. The sclerotia were white at first and flat, later turning black,
and as the culture became older, curling up and becoming crust-like.
All four of the forms mentioned above showed these same character-
istics, altho they were originally obtained from widely separated locali-
ties. (See Fig. 22.) The strain from onion produced sclerotia which
were entirely different from those of other strains in that they were
small (.5 to 1 millimeter in diamater), perfectly round, bright colored,
and developed submerged in the medium. (See Fig. 23.) The strains
"Buckwheat," "Carnation R.O.," " Gypsophila, " and "Sedum"
rarely produced sclerotia in culture. Repeated observations showed
that this loss of power to produce sclerotia was the first sign of the de-
generation and loss of virulence of the strain.
All the other strains studied produced sclerotia which were at first
white, later becoming brown. Altho the sclerotia from the strain from
potato are similar to those from carnation when grown on culture
media, on the potato tuber they are entirely different. For the most
part the Rhizoctonia sclerotia on potato tubers which the writer has
examined are flat and hard, have a black luster, and are in many re-
spects like the sclerotia produced in culture media by the strains from
eggplant, lettuce, etc.
The only conclusion that can be drawn from this study of the
growth of Rhizoctonia Solani on media is that the strains are very
variable, those from the same host often producing a different growth,
even; on the same media, and- that the differences in various cultural
characters which are shown by strains from different hosts are no
greater than differences which may be manifested by two different
strains isolated from the same host or by the same strain at different
ages.
MEASUREMENT OF MYCELIAL CELLS
It was rather difficult to choose a standard in the measurement of
the mycelial cells, because the cells varied in size at different ages and
on different media. Finally the following standard was chosen:
Hyphae from the outer edge of a twenty-four hour old culture on
green-bean agar were selected at random. The length and width of
a cell from which the branch arose nearest the tip of the hypha, and
1916]
PARASITIC RHIZOCTONIAS IN AMERICA
371
the distance on the inner side from the parent hypha to the first sep-
tum of the branch, were measured. Ten cells of each strain were
measured, and the averages of these measurements used for compari-
son.
As shown in Table 12, the measurements varied considerably, and
this was true even with strains from the same host. In the three car-
nation strains measured, the length of the mycelial cells varied from
TOfji. to 181. 1^, a difference of 111.7/x. However, the average of ten
measurements brings the difference down to some extent. A still more
striking difference was noted in the strains from Dianthus, where
the smallest reading was 50//, and the largest 215/*, a difference of 165/A.
Similar differences were also found in comparing the two other meas-
urements.
In all cases, altho the table does not bring out this point, different
measurements of the cells of the various strains overlapped. For ex-
TABLE 12. — MEASUREMENTS OF MYCEIJAL CELLS OP EHIZOCTONIA
Strain
Length
of cell
Width
of cell
Distance from
cell to septum
of branch
Alfalfa
u
152.04
H
5.76
V.
10.08
Alternanthera R.A.C
113.40
3.92
6.72
" B A F
124.60
4.94
9.32
107.80
4.83
7.98
180.04
6.57
13.08
Beet
77.92
4.34
6.52
Carnation R H
116.09
4.59
10.83
' ' R.M.2
141.40
5.60
10.49
' > E.F.2
128.15
5.19
10.92
Carrot
116.64
4.42
9.60
Cauliflower
119.64
4.20
9.60
Chenopodium
175.56
5.43
11.20
Clover
88.20
5.32
8.53
Coleus I
117.60
5.04
10.21
Coleus II
133.28
4.97
10.22
Corn
101 64
4.39
9.24
Cotton I
65.24
5.50
10.18
Dianthus barbatus S.M
N.P
113.12
161.00
5.58
5.27
9.44
10.58
sequeri
131.60
6.29
6.44
plumarius . .
166 95
5.65
13.44
Eggplant I
13234
4.20
11.65
" II
148 88
5.60
9.57
Gypsophila repens
122 08
3.55
8.03
Lavatera
91 84
5 89
9 18
Lettuce
119 92
439
10 54
Poinsettia
126 20
3.44
7.92
Salvia
111 16
5 01
9 93
Sedum
90 80
4 48
7 00
Sugar cane
113 12
409
657
Sweet pea
13048
5 04
854
Thistle
138.08
4.62
11.48
372 BULLETIN No. 189 [June,
ample, while the average length of a cell from "Cotton I" was only
65/t, the largest reading was 127. .V, which was higher than the small-
est measurement of a cell of the strain " Chenopodium, " whose aver-
age reading was 110/u higher than that of "Cotton I." If measure-
ments are made of hyphae forty-eight hours old, the differences are still
more striking, even in the same strain.
Hence, on the measurement of mycelial cells of Rhizoctonia Solani,
as on the study of the growth on media, no conclusions can be based in
regard to distinguishing the strains of this difficult species.
SOIL SURVEY OF RHIZOCTONIA
As shown in Table 1, Rhizoctonia Solani has been observed in al-
most every state in the Union, and causes injury to a large number of
plants under various conditions and in widely different types of soils.
To determine to how great an extent Rhizoctonia is actually present
in the soil, several surveys were made at the University of Illinois in
fields containing a variety of plants.
Survey of ihe Perennial Garden, Horticultural Grounds, April 28
to May 1, 1914. — During the summer and fall of 1913, Rhizoctonia
was isolated from a number of perennial plants in the garden. To
determine whether the fungus lived on the dead parts of the plants
or in the soil or both during the winter season, a survey was made the
following spring.
Since it is somewhat difficult to isolate Rhizoctonia directly from
the soil by means of soil cultures, the following method was devised
to determine its presence in the soil: Small patches of ground were
selected over the field about twenty feet apart, so that the results might
give a fair idea of the distribution of the fungus. Each space was
cleared except for a small living plant, and the soil thoroly watered.
Three sheets of moistened filter paper were then placed on the
ground over the plant. To prevent evaporation, a small flat with a
layer of wet moss attached to the bottom was placed over the paper.
The flats had previously been sterilized in formalin (1-100) and the
moss sterilized in the autoclave. Thru several small holes in the bot-
tom of the flat, water was added to the moss from day to day to keep
it moist. At the end of the fifth day the plant parts were removed
to the laboratory.
The presence of the fungus was determined by means of pure cul-
tures and by microscopic observation. Where the identification de-
pended solely on microscopic observations, the material was left in a
covered dish for several days until the strands of the fungus became
older, when they could be distinguished more readily by their color.
In thirteen cases out of sixteen Rhizoctonia was found present on
the dead or living pieces of plants placed in contact with the soil;
PARASITIC RHIZOCTONIAS IN AMERICA
373
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374 BULLETIN No. 189
hence we may conclude that this fungus was very abundant both in the
soil and on the plant parts in contact with the soil.
Survey of Plot Used for Field Inoculation Experiments, May 6
to May 11, 1914. — This plot, formerly used by the Agronomy Depart-
ment, had been under cultivation for a number of years. The pre-
vious season the field had been in potatoes and corn. The old potato
stalks were left scattered over the field during the winter.
A survey of the plot was made before plowing, following the same
method as was used as in the preceding experiment. Sixteen flats
were set out twenty-five feet apart. After five days an examination for
the presence of Rhizoctonia was made. By microscopic examination
and pure cultures, Rhizoctonia was detected in ten trials out of sixteen
on this plot.
Survey of Agronomy Plots on North Farm, September 26 to Octo-
ber 2, 1914. — Here a more extensive survey was conducted. The
agronomy plots on the North Farm were chosen for this purpose be-
cause of the fact that they had been under continuous cultivation
since 1895, and showed the effects of different methods of soil treat-
ment, various systems of crop rotation, and the application of differ-
ent kinds of food. (For treatments and rotations used, see Fig. 24.)
These plots are also typical of the prairie soil, which represents the
most extensive and important type of soil in Illinois.
The procedure followed in this survey was modified as follows:
In stead of a flat, a seven-inch flower pot, which could be easily steri-
lized and dried, was employed. Small cheesecloth bags were filled with
sphagnum moss ; these were sterilized in the autoclave. When ready
for use, the bags were moistened and placed in the bottom of the pots
and secured in such a way that they remained in position when the
pots were inverted. A small patch of soil, one in each plat, was lev-
eled off, only a small living plant or some plant debris being left.
Several thicknesses of moistened filter paper were then laid over the
spot, and a flower pot was placed over the whole. The pot was pushed
into the ground about three inches and the soil heaped up around it
on the outside. The pots were left in this condition about one week,
during which time the moss was moistened at intervals. Conditions
were very favorable to the growth of Rhizoctonia if it was present
in the soil. When the pots were lifted, the plant parts or debris with
some of the soil were wrapped in the filter paper and placed under
bell jars. The contents of the papers were then examined for the
presence of Rhizoctonia.
These plots showing the effects of diverse treatments yielded R.
Solani in sixty-four trials out of seventy. The six negative results
were scattered over the field, so that no correlation between the treat-
ment of the plot and the presence of Rhizoctonia can be said to exist,
1916] PARASITIC BHIZOCTONIAS IN AMERICA 375
The results of these experiments admit of no question as to the
presence of the fungus Khizoctonia Solani in the soil in the vicinity
of Urbana.
PARASITISM OF RHIZOCTONIA SOLANI KUHN
That R. Solani is an active parasite under certain conditions would
never be questioned by anyone who had seen a severe attack of car-
nation stem rot in the field or greenhouse. In the cutting bench
this fungus causes damping-off of cuttings in an incredibly short time,
while seedlings damp oft' almost as fast. At times Rhizoctonia causes
considerable loss in potato fields. In fact, it may become epidemic
and cause serious injury to most of the field, vegetable, and floricul-
tural crops.
The epidemics are apparently due to a combination of factors,
such as the presence of a virulent strain of the fungus, a susceptible
variety of plant, and optimum conditions of temperature and moisture
for infection and development. Under ordinary conditions most of
the strains appear to be weak parasites.
The apparently universal presence of Rhizoctonia in the soil,
where it can live indefinitely on dead organic matter under ordinary
conditions, makes it a dangerous fungus. The fact that it shows no
marked specialization and can attack a large variety of weeds assists
in harboring the fungus and in keeping up its virulence. The sclero-
tia and mycelium can live under adverse conditions for several years.
Transfers from soil cultures started in December, 1911, kept in the
laboratory, and allowed to dry out, yielded pure cultures as late as
July, 1914. Soil cultures left in the field during the entire winter
yielded the fungus in the spring.
In all but one of the experiments inoculation was brought about
without wounding the plants in any way, in many cases the fungus
being simply mixed with the soil in which the plants were growing.
The results furnish convincing proof of the parasitism of the fungus.
The conditions under which all strains manifested their greatest para-
sitism were primarily a high temperature (above 88° F.) and a soil
moisture content either too low or too high for the best development of
the plant. When carnation plants growing in soil inoculated with
Rhizoctonia were given a heavy watering and the soil was then allowed
to dry out, they were killed more rapidly than plants growing under
the same conditions but in continually over-watered soil. Plants
watered normally died off slowly and the percentage of loss was very
much less.
Repeated observations in greenhouse and field have shown that a
certain amount of the mycelium must be present before the fungus is
able to attack and kill the plant. A small amount of mycelium has
always been observed around a carnation plant in the bench a week
376 BULLETIN No. 189 [June,
or more before the plant showed any signs of being diseased. In fact,
a certain amount of mycelium is always present in the carnation soil
in the greenhouse, but it is only when the temperature is high that
the fungus is able to attack the plants. This explains why stem rot
of carnations is more severe during the summer months than in the
winter. (See Experiment 6, page 349.) In the field similar conditions
are necessary to result in infection of a plant.
Investigations to determine how much vigor the mycelium must
attain before the fungus can attack a plant are now in progress, as
is also a histological and enzymatic study.
SUMMARY
1. At the present time there are recognized in America two
species of truly parasitic Rhizoctonias : The common form, RMzoctonia
Solani Kiihn (Corticium vagum B. & C.), widely distributed and oc-
curring on a great number of hosts; and R. Crocorum (Pers.) DC.,
with a limited distribution on alfalfa and potato tubers. A third
RMzoctonia, Corticium ochraleucum (Noack) Burt, is found on the
leaves of pomaceous fruit trees, while a fourth species isolated from
damped-off onion seedlings is of questionable parasitism.
2. The plants thus far listed as more or less subject to attacks of
RMzoctonia Solani Kiihn in the United States number about 165
species. All the more important families of dicotyledons are included
in this list, as well as a number of monocotyledons, several gymno-
sperms, and Equisetum. Most of the Agricultural plants, vegetable
and field crops, herbaceous plants, and many weeds are susceptible to
attacks of this fungus.
3. The symptoms produced by Rhizoctonia Solani Kiihn in nat-
ural infection are largely similar when appearing on the same type
of host. The damping-off of seedlings and cuttings of various plants
is identical, as is the rotting of a number of root crops. In most her-
baceous plants a stem rot is produced, the symptoms of which are also
identical on the various hosts. On very resistant plants lesions only
are formed ; these are apparently the same on the different hosts.
4. From these inoculation experiments with a large number of
different types of plants, we must conclude that all the strains studied,
which were obtained from a wide range of hosts of diverse geographi-
cal origin, can attack the same species of plant and produce the same
characteristic symptoms. No marked specialization was noted in any of
the strains. Thus all the strains studied can be included under one
form, Rhizoctonia Solani Kiihn. The inoculation experiments show
further that the virulence of R. Solani is very variable, as is also the
degree of resistance of the various host plants, both depending on a
number of varying factors.
1916] PARASITIC KHIZOCTONIAS IN AMERICA 377
5. Studies of the growth of Rliizoctonia Solani Kiihn on media
show that the strains are very variable, those from the same host
often producing a different growth even on -the same media, and that
the differences in various cultural characters which are shown by
strains from unlike hosts are no greater than the differences which
may be manifested by two different strains isolated from the same host
or by the same strain at different ages.
6. Measurements of mycelial cells of Rhizoctonia Solani Kiihn
showed such large variations, not only between strains from different
hosts but also between different strains from the same host, that no
standard could be determined on for distinguishing the different
strains.
7. By means of a local soil survey, it was found that RJiizoctonia
Solani Kiihn is abundant in cultivated land, where it may live either
on dead organic matter in the soil or on weeds and other plants.
8. A certain vigor of mycelium must be attained before Rliizoc-
tonia Solani Kiihn is able to attack a plant. A high temperature
(88° F.), together with either too little or too much moisture, deter-
mines to a large degree the virulence of the strains. It is only under
certain conditions that the fungus becomes a dangerous parasite.
The writer gratefully acknowledges his indebtedness to Dr. F. L.
Stevens, Professor of Plant Pathology, and to Dr. J. T. Barrett, for-
mer Chief Assistant in Botany, for their kind assistance and encour-
agement. He wishes also to thank Professor H. B. Dorner, Assistant
Chief in Floriculture ; Mr. C. C. Rccs, formerly Assistant in Floricul-
tural Pathology; and other members of the Division of Floriculture
for assistance rendered during the progress of this work.
378 BULLETIN No. 189 [June,
APPENDIX
COMPOSITION OF MEDIA USED IN EXPERIMENTS
Corn-Meal Agar (Shear*). — To 4 teaspoonfuls of corn meal add 1 liter of dis-
tilled water. Keep in water bath for one hour at a temperature below 60°C.
Strain thru gauze, and to the filtrate add 1 percent agar flour. Steam three-quarters
of an hour. Filter thru paper tube and place in autoclave for 15 minutes at
115° C.
Green-Bean Agar. — 300 grams young string beans cooked in 500 cc water
for one hour and strained thru cloth. 15 grams agar (powdered) melted in 500 cc.
water. Mix the two, add enough water to make 1000 cc., add 6 to 8 grains egg
albumen, and boil in autoclave. Filter thru cotton.
Oat Agar (Clinto^). — 200 grams oats ground fine thru a coffee mill and
soaked in 500 cc. water for one hour. 15 grams agar melted in 500 cc. water and
strained thru cheesecloth. Mix the two but do not filter, since the most nutrient
part of the medium would be lost.
Potato Agar. — 300 grams peeled potatoes, sliced as thin as possible and cooked
in 500 cc. water for one hour. Strain thru cloth. 15 grams agar (powdered)
melted in 500 cc. water. Mix the two and add enough water to make 1000 cc.
Add 6 to 8 grams egg albumen (powdered) and boil in autoclave for a short time.
Filter thru cotton.
Potato-Glucose Agar.— 290 grams peeled potatoes, sliced as thin as possible
and cooked in 500 cc. water for one hour. Strain thru cloth and add 20 grams of
glucose. 15 grams agar (powdered) melted in 500 cc. water. Mix the two, add
enough water to make 1000 cc., add 6 to 8 grams egg albumen (powdered), and
boil in autoclave for short time. Filter thru cotton.
Agar (Cookc)
Water
1000.00 cc.
ims
Aear
15.00 grf
Glucose
20.00
Ammonium nitrate
1.00
Potassium nitrate
1.00
Ammonium sulfate
1.00
Magnesium sulfate
25
Dipotassium phosphate
25
Calcium chlorid". .
.01
GROWTH ON MEDIA
' ' ALFALFA ' '
On Corn-Meal Agar. — Growth poor and rather slow. Mycelium white, fine,
submerged, and scarcely visible. No coloring of the medium. No zonation.
On Green-Bean Agar. — Growth poor and slow. Mycelium white, fine, loose,
and becoming somewhat tufted. Zonation. Like strain from corn.
On Potato Agar. — Growth rather slow. Characterized by the dark color
of the mycelium and the turning of the medium to a darker color. Hyphsu loose,
fine, and practically all submerged. No zonation.
»U. S. Dept. Agr., Bur. Plant Indus., Bui. 252, 15. 1913.
bConn. Sta. Rpt. (1909-10), 32, 760. 1911.
cDel. Sta. Bui. 91, 12. 1911.
dOmitted from formula used.
1916] PARASITIC BHIZOCTONIAS IN AMERICA 379
Stewart,1"5 in reporting the damping-off of alfalfa seedlings in the greenhouse
and the crown rot of mature plants in the field, states that "the one causing
dampiner-off of seedlings in the greenhouse is different from the one found in the
field. When grown on potato agar (slightly acid, neutral, or slightly alkaline),
the former produces a conspicuous dark brown discoloration of the medium, whereas
the latter discolors it only slightly. This character may be useful in the identi-
fication of the damping-off Rhizoctonia. Such discoloration of the medium is not
common among the species of Ehizoctonia. " It is interesting to note that the
strain obtained from Louisiana causing a damping-off of alfalfa seedlings and a
number of other strains showed the same discoloration as the one studied by
Stewart.
On Agar XII. — Growth fair. Few loose, erect hyphse, becoming denser and
finally forming an indistinct zone.
" ALTERNANTHERA B. A. C."
On Corn-Meal Agar. — Growth very rapid, but not dense. Mycelium white,
loose, aerial, and fine. No zonation.
On Green-Bean Agar. — Growth good. Mycelium tufted and compact, not
turning darker. Zonation somewhat distinct at end of third day. Three zones
present.
On Oat Aoor. — Growth rapid. Mycelium flat, and very compact, forming a
mat over the surface. Zonation.
On, Potato Agar. — Growth very rapid, with zone formation beginning im-
mediately. Mycelium all aerial and growing very compactly. Plate was covered
at end of forty-eight Lours and showed two distinct zones and one indistinct.
On Potato-Glucose Agar. — Growth rapid; plate covered in forty-eight hours.
Mycelium white, loose, and flaky. Zonation.
On Agar XII. — Growth good. Mycelium white, fine, compact, and somewhat
flaky. Zonation.
. ' ' ALTERNANTHERA E. A. F. ' '
On the various media this strain produced the same kind of growth in each
case as the strain from the cutting bench, except that it grew more rapidly.
' ' ASTER ' '
On Green-Bean Agar. — Growth fair. Mycelium white, loose, regular, :oid flat,
becoming somewhat tufted. Four zones formed at end of the fourth day.
On Oat Jf/er.— Growth fair. Mycelium white, loose, flat, and regular, be-
coming fluffy and tufted. Like strain ' ' Carnation E. F. " Five zones at end of
fourth day.
On Potato-Glucose Agar. — Growth slow and poor. Mycelium mostly submerged
and turning brown. No zonation.
On Agar XII. — Growth fair. Mycelium white, loose, flat, and regular, be-
coming somewhat tufted. Zonation.
"BEAN"
On Corn-Meal Agar. — Growth very poor; scarcely visible. Mycelium white,
fine, somewhat aerial. No zonation.
On Grcen-'Bean Agar. — Growth slow. Mycelium fine, aerial, loose, and white,
darkening with age. Two zones formed, but not very distinct; otherwise like the
strain from carrot.
On Potato Agar. — Growth fair. Mycelium fine, more or less submerged, and
discoloring the medium only slightly. No zonation.
380 BULLETIN No. 189 [June,
On Agar XII. — Growth rapid. Mycelium somewhat tufted and dense. Three
distinct zones present.
"BEET"
On Green-Bean Agar. — Growth good. Mycelium flat and compact. Several
Hones present.
' ' BEGONIA ' '
On Corn-Meol Agar. — Growth fair. Mycelium rather compact and white. No
zonation.
On Green-Bean Agar. — Growth fair. Mycelium white, tufted, and compact.
Zonation indistinct.
On Potato Agar. — Growth fair. Mycelium compact, dense, and white; me-
dium turning dark. Zonation.
On Agar XII. — Growth scant. Mycelium white, fine, and loose. No zonation.
' ' CARNATION U.K."
On Corn-Meal Agar. — Growth good. Mycelium white, making a rather dense
growth for corn-meal agar. Zonation indistinct.
On Green-Bean Agar. — Growth good. Like strain "Carnation R. H. "
On Oat Avar — Growth good. Mycelium white, loose, edge tufted. Zonation.
On Potato Agar. — Growth poor. Mycelium loo?e and scattering, medium turn-
ing darker. Zonation indistinct.
On Agar XII. — Growth poor. Mycelium white, loose, and scattered; edge
irregular. Zonation indistinct.
"CARNATION B. H."
On Corn-Meal Aaar. — Growth fair. Mycelium white, fine, and in loose strands ;
rather dense at center. No zonation.
On Grccn-Bcan Agar. — Growth good. Mycelium dark at center, loose, and
tufted; edge irregular. Zonation very characteristic of the strains isolated from
diseased carnation plants.
On Potato Agar. — Growth poor. Mycelium fine and scattered; edge irregular.
Mycelium causing a characteristic browning of the medium. Zonation indistinct.
On Agar XII. — Growth poor. Mycelium white, fine, loose, and scattered. No
zonation.
"CARNATION E. S."
On Corn-Meal Agar. — Growth fair. Mycelium white, fine, but rather dense at
center; edge regular. Zonation.
On Green-Bean Agar. — Growth good. Mycelium loose, white, and tufted; edge
regular. Later, mycelium turned brown. Zonation somewhat indistinct.
On Potato Af;ar. — Growth poor and scant. Mycelium producing a distinct
browning of the agar. Zones indistinct.
On Agar XII. — Growth poor. Mycelium white, scant, loose, and flat. Zonation.
' ' CARNATION E. F. "
On Corn-Meal Agar. — Growth good. Mycelium white, loose, and somewhat
tufted. No zonatiou.
On Green-Bean Agar.— Growth fair. Mycelium white, compact, and tufted.
Zonation somewhat indistinct.
1916] PARASITIC RHIZOCTONIAS IN AMERICA 381
On Oat Agar. — Growth good. Mycelium white, loose, flat, and fairly dense;
edge tufted. Zonal ion.
On Potato Agar. — Growth poor. Mycelium scant, like that produced by strains
from carnation.
On Potato-Glucose Agar. — Growth poor. Mycelium white, loose, scattered,
and somewhat flaky ; edge very irregular. Zonation.
On. Agar XII. — Growth poor. Mycelium white, fine, loose, flat, and scatter-
ing; edge very irregular. Zonation indistinct.
•
' ' CARNATION R.M.2 ' '
On Corn Meal Agar. — Growth good. Mycelium white, tufted, and somewhat
compact. No zonation.
On Green-Bean Agar. — Growth fair. Mycelium white, tufted, ard compact.
Zonation indistinct.
On Oat Agar. — Growth fair. Mycelium white, loose, and somewhat flaky at
center; edge loose and irregular. Zonation.
On Potato Agar. — Growth poor. Mycelium loose and fine. Zonation indis-
tinct.
On Potato-Glucose Agar. — Growth fair. Mycelium brown, loose, und flat;
edge loose and tufted. No zonation.
On Agar XII. — Growth fair. Mycelium white, loose, flat, and scattered. No
zonation.
"CARNATION B.D.C."
On Corn-Meal Agar. — Growth good. Mycelium white, loose, tufted, and rather
dense. No Donation.
On Green Tican Agar. — Growth good. Mycelium white, loose, tufted, and
dense. Zonation distinct.
On Oat Agar. — Growth fair. Mycelium white, somewhat dense at center, and
more tufted at edge. Zonation.
On Potato Agar. — Growth poor. Mycelium loose and flat, darkening slowly
with age. Zoi.ation indistinct.
On Potato-Glucose Agar. — Growth fair. Mycelium white, flat, and flaky at
center.; edge loose and fluffy. Zones numerous and distinct.
On Agar XII. — Growth poor. Mycelium white, somewhat flaky at center; edge
irregular an-1 scattered. Zonation.
' ' CARROT ' '
O.i Corn-Meal Agai. — Growth good. Mycelium white, fine, and somewhat com-
pact. No zonation.
On Green-Bean Agar. — Growth poor. Mycelium loose, flat, and somewhat
fluffy; white at first, followed by purplish tinge. Zonation not very distinct.
On Oat Agar. — Growth fair. Mycelium white, fine, loose, and flat. Zonation
indistinct.
On Potato Agar. — Growth fair. Mycelium dark, dense, and compact. Zona-
tion indistinct.
On Potato-Glucose Agar. — Growth fair. Mycelium dark, loose, flat, and flaky.
Four to six zones present.
On Agar XII. — Growth slow. Mycelium white, loose, and somewhat flaky.
Zonation.
382 BULLETIN No. 189 [June,
1 ' CAULIFLOWER ' '
On Corn Meal Agar. — Growth poor. Mycelium white, loose, and scant. No
zonation.
On Green-Sean Agar. — Growth good. Mycelium white, tufted, and compact;
edge regular. Zonatioii.
On Oat Agar. — Growth good. Mycelium white, fine, loose, flat, and dense,
running out in characteristic strands. No zonation.
On Potato-Glucose Agar. — Growth fair. Mycelium dark, loose, flat, and flaky.
One zone at outer edge.
On Agar XII. — Growth good. Mycelium white, loose, flat, and flaky. Zonation.
" CHENOPODIUM "
On Green-Bean Agar. — Growth good. Mycelium white, flat, radial, and com-
pact. No zonation.
"CLOVER (RED)"
On Green-Bean Agar. — Growth good. Mycelium flat and compact. Zonation.
"COLEUS I"
On Corn- Meal A gar. — Growth good. Mycelium white, loose, and somewhat
compact. No zonal iou.
On Green-Bean Agar. — Growth good. Mycelium white, tufted, and compact.
Zonation indistinct.
On Oat Agar. — Growth good. Mycelium white, loose, and flat; edge fluffy.
No zonation.
On Potato Agar. — Growth fair. Mycelium loose and tufted, turning darker
with age. No zonation.
On Potato-Glucose Agar. — Growth fair. Mycelium dark, loose, and flaky;
edge irregular. Zonation.
On Agar XII. — Growth good. Mycelium loose, dense, and white. No zonation.
' ' CORN ' '
On Corn-Meal Agar. — Growth poor. Mycelium white, fine, and scattered. No
zonation.
On Green-Bean Agar. — Growth fair. Mycelium loose at edge and somewhat
compact, turning darker with purplish tinge. Two distinct zones.
On Potato Agar, — Growth fair. Mycelium dense and compact. Mycelium and
medium turned dark. Zonation indistinct.
On Agar XII. — Growth fair. Mycelium white, loose, tufted, and rather dense
at center. Zonation.
"COTTON I"
On Green-Bean Agar. — Growth fair. Mycelium loose, tufted, dense, and white.
Two zones present. • .
On Oat Agar. — Growth good. Mycelium white, loose, flat, dense, and radial,
later taking on a wrinkled appearance. No zonation.
On Potato-Glucose Agar. — Growth fair. Mycelium white, flat, dense, flaky,
and regular; loose at edge. Zonation indistinct.
1916] PARASITIC EHIZOCTONIAS IN AMERICA 383
On Agar XII. — Growth fair. Mycelium flat, somewhat dense, flaky, and
white at center; edge loose. Two distinct zones.
"COTTON II"
On Green-Bean Agar. — Growth fair. Mycelium loose, tufted, and fairly dense,
later turning brown. Two zones present.
On Oat Agar. — Growth fair. Mycelium white, fine, loose, and flat, forming a
mat over surface of the medium. One zone present.
On Potato-Glucose Agar. — Growth fair. Mycelium loose, flat, and fairly dense ;
edge irregular. Later both mycelium and medium turned brown. Two zones
present.
On Agar XII. — Growth fair. Mycelium white, loose, and somewhat tufted.
Three zones present.
"DlANTHUS BARBATUS N.P. "
On Green-Bean Agar. — Growth fair. Mycelium tufted and compact. Zonation
indistinct.
"DlANTHUS BARBATUS S.M. "
On Green-Bean Agar. — Growth good. Mycelium tufted and compact. Zona-
tion rather indistinct.
' ' DlANTHUS PLUMARIUS ' '
On Green-Bean Agar. — Growth good. Mycelium loose, white, and somewhat
tufted; edge regular. Zonation characteristic of the carnation strains.
"DlANTHUS SEQUERl"
On Green-Bean Agar. — Growth good. Mycelium loose, white, and somewnut
fluffy; edge regular. Zonation characteristic of carnation strains in all respects.
' ' EGGPLANT I ' '
On Corn-Meal Agar. — Growth poor. Mycelium white, fine, and mostly sub-
merged. No zonation.
On Green-Bean Agar. — Growth good. Mycelium white, flat, radial, compact,
and dense. One zone at center.
On Oat Agar. — Growth fair. Mycelium white, loose, flat, interwoven, and
somewhat tufted. Zonation.
On Potato Agar. — Growth good. Mycelium dark, compact, dense, and radial.
No zonation.
On Potato-Glucose Agar. — Growth fair. Mycelium in radial strands, flat, and
white. No zonation.
On Agar XII. — Growth fair. Mycelium white, flat, dense, and compact.
One zone present.
' ' GYPSOPHILA ' '
On Green-Bean Agar. — Growth fair. Mycelium white, fluffy, and somewhat
compact. Zonation very characteristic of strains from carnation.
' ' LAVATERA ' '
On Green-Bean Agar. — Growth good. Mycelium white, loose, and tufted; edge
even. Several zones present.
384 BULLETIN No. 189 [June,
"LETTUCE"
On Corn-Meal Agar. — Growth fair. Mycelium white, fine, slightly aerial, az<l
somewhat flaky. No zonation.
On Green-Bean Agar. — Growth good. Mycelium white, loose, flat, and rather
dense, running out in strands. One indistinct zone present.
On Oat Agar. — Growth fair. Mycelium white, loose, flat, interwoven, and
somewhat tufted. One zone present.
On Potato Agar. — Growth fair. Mycelium dark, fine, and practically all sub-
merged. No zonation.
On Potato-Glucose Agar. — Growth good. Mycelium white and flat, running
out in radial strands. No zonation.
On Agar XII. — Growth good. Mycelium white, loose, flat, and rather dense.
No zonation.
"ONION"
On Green-Bean Agar. — Growth fair. Bright colored mycelium, fine and sub-
merged at center; a little aerial mycelium at the outer edge, where it was some-
what loose. No zonation.
On Potato Agar. — Growth fair. Mycelium fine, scarcely visible, and of a
bright color. No zonation.
On Agar XII. — Growth fair. No aerial mycelium. No zonation.
"POIXSETTIA"
On Corn-Meal Agar. — Growth fair. Mycelium white, dense, fluffy, and com-
pact. Zonation indistinct.
On Green-Bean Agar. — Growth fair. Mycelium white, loose, compact, and
fluffy. No zonation.
On, Oat Agar. — Growth good. Mycelium white, loose, flat, and radial; edge
somewhat fluffy. No zonation.
On Potato Agar. — Growth fair. Mycelium somewhat flaky and compact. Three
zones present.
On Potato-Glucose Agar. — Growth fair. Mycelium brown and flat at center;
outer edge white, loose, and somewhat flaky. Zonation indistinct.
On Agar XII. — Growth fair. Mycelium white, flat, dense, and radial, like
alternanthera. One zone.
"POTATO R. SOL."
On Corn-Meal Agar. — Growth fair. Mycelium fine and flat. No zonation.
On Green-Bean Agar. — Growth fair. Mycelium loose at edge, compact and
fluffy at center. Several zones present, two distinct.
On Potato Agar. — Growth fair. Mycelium white and fluffy. One zone at center.
On Agar XII. — Growth poor. Mycelium mostly submerged and somewhat com-
pact; flaky at center. Zonation.
"POTATO K.P.O."
On Corn-Meal Agar. — Growth fair. Mycelium white, fine, and rather scant.
No zonation.
On Green-Bean Agar. — Growth good. Mycelium loose at edge, flat, dense,
somewhat fluffy, and rather dark. Three zones present. Growth very much like
strains from carnation.
W16] PARASITIC BHIZOCTOXIAS ix AMERICA 385
On Potato Agar. — Growth fair. Mycelium dark, loose, and fluffy. Zonation
distinct.
On Potato-Glucose Agar. — Growth fair. Mycelium white, flat, loose at edge,
and flaky at center. Three zones present.
On Agar XII. — Growth very slow. Mycelium white, dense, and bushy, form-
ing a tuft at the center. No zonation.
"SALVIA"
On, Green-Bean Agar. — Growth good. Mycelium white, tufted, and compact.
•Zonation indistinct.
On Oat Agar. — Growth good. Mycelium white, loose, flat, rather dense, and
radial. Zonation indistinct.
On Potato-Glucose Agar. — Growth fair. Mycelium white and flaky at center;
edge loose and tufted. Zonation indistinct.
On Agar XII. — Growth good. Mycelium white and flaky at center; edge loose
and tufted. Zonation indistinct.
"SEDUM"
On Green-Bean Agar. — Growth good. Mycelium flat and compact. One zone
present. '
' ' SUGAR CANE ' '
On Corn-Meal Agar. — Growth fair. Mycelium white, fine, and scarcely visi-
ble. No zonation. .
On Green-Bean Agar. — Growth fair. Mycelium white, loose, and tufted. Zones
present.
On Potato Agar. — Growth fair. Mycelium white, fine, and practically all sub-
merged. Two indistinct zones present.
On Agar XII. — Growth fair. Mycelium white, fine, and running out in strands
from the center. No zonation.
"SWEET PEA"
On Green-Bean Agar. — Growth good. Mycelium flat and compact. One zone
present. In many respects like strain from carnation.
' ' THISTLE ' '
On Corn-Meal Agar. — Growth fair. Mycelium white, running out in strands;
flat at center, and somewhat loose at edge. No zonation.
On Green-Bean Agar. — Growth good. Mycelium white, flat, radial, and com-
pact at center; edge somewhat loose and fluffy. Zonation indistinct.
On Oat Agar. — Growth good. Mycelium white, flat, dense, and radial. No
zonation.
On Potato Agar. — Growth fair. Mycelium white, flat, and somewhat compact,
running out in strands. No zonation.
On Potato-Glucose Agar. — Growth fair. Characterized by a white, radial, flat
mycelium. No zonation.
On Agar XII. — Growth fair. Mycelium white, flat, compact, and flaky at cen-
ter, becoming looser at edge. No zonation.
386 BULLETIN No. 189 [June,
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